What is MySQL?

  • MySQL is a relational database management system
  • MySQL is open-source
  • MySQL is free
  • MySQL is ideal for both small and large applications
  • MySQL is very fast, reliable, scalable, and easy to use
  • MySQL is cross-platform
  • MySQL is compliant with the ANSI SQL standard

What is RDBMS?

RDBMS stands for Relational Database Management System.

RDBMS is a program used to maintain a relational database.

RDBMS is the basis for all modern database systems such as MySQL, Microsoft SQL Server, Oracle, and Microsoft Access.

RDBMS uses SQL queries to access the data in the database

What is a Database Table?

A table is a collection of related data entries, and it consists of columns and rows.

A column holds specific information about every record in the table.

A record (or row) is each individual entry that exists in a table.

Look at a selection from the Northwind "Customers" table:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico

The columns in the "Customers" table above are: CustomerID, CustomerName, ContactName, Address, City, PostalCode and Country. The table has 5 records (rows).

What is a Relational Database?

A relational database defines database relationships in the form of tables. The tables are related to each other - based on data common to each.

Look at the following three tables "Customers", "Orders", and "Shippers" from the Northwind database:

Customers Table

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico

The relationship between the "Customers" table and the "Orders" table is the CustomerID column:

Orders Table

OrderID CustomerID EmployeeID OrderDate ShipperID
10278 5 8 1996-08-12 2
10280 5 2 1996-08-14 1
10308 2 7 1996-09-18 3

The relationship between the "Orders" table and the "Shippers" table is the ShipperID column:

Shippers Table

ShipperID ShipperName Phone
1 Speedy Express (503) 555-9831
2 United Package (503) 555-3199
3 Federal Shipping (503) 555-9931

What is SQL?

SQL is the standard language for dealing with Relational Databases.

SQL is used to insert, search, update, and delete database records.

How to Use SQL

The following SQL statement selects all the records in the "Customers" table:

Example

SELECT * FROM Customers;

Keep in Mind That...

  • SQL keywords are NOT case sensitive: select is the same as SELECT

In this tutorial, we will write all SQL keywords in upper-case.

Semicolon after SQL Statements?

Some database systems require a semicolon at the end of each SQL statement.

Semicolon is the standard way to separate each SQL statement in database systems that allow more than one SQL statement to be executed in the same call to the server.

In this tutorial, we will use semicolons at the end of each SQL statement.

Some of The Most Important SQL Commands

  • SELECT - extracts data from a database
  • UPDATE - updates data in a database
  • DELETE - deletes data from a database
  • INSERT INTO - inserts new data into a database
  • CREATE DATABASE - creates a new database
  • ALTER DATABASE - modifies a database
  • CREATE TABLE - creates a new table
  • ALTER TABLE - modifies a table
  • DROP TABLE - deletes a table
  • CREATE INDEX - creates an index (search key)
  • DROP INDEX - deletes an index

MySQL CREATE DATABASE Statement

Syntax

CREATE DATABASE databasename;

The MySQL DROP DATABASE Statement

Syntax

DROP DATABASE databasename;

The MySQL CREATE TABLE Statement

Syntax

CREATE TABLE table_name ( column1 datatype, column2 datatype, column3 datatype, .... );

Example

CREATE TABLE Persons ( PersonID int, LastName varchar(255), FirstName varchar(255), Address varchar(255), City varchar(255) );

Create Table Using Another Table

A copy of an existing table can also be created using CREATE TABLE.

The new table gets the same column definitions. All columns or specific columns can be selected.

If you create a new table using an existing table, the new table will be filled with the existing values from the old table.

Syntax

CREATE TABLE new_table_name AS
SELECT column1, column2,...
FROM existing_table_name
WHERE ....;

The following SQL creates a new table called "TestTables" (which is a copy of the "Customers" table):

Example

CREATE TABLE TestTable AS
SELECT customername, contactname
FROM customers;

The MySQL DROP TABLE Statement

Syntax

DROP TABLE table_name;

MySQL TRUNCATE TABLE

The TRUNCATE TABLE statement is used to delete the data inside a table, but not the table itself.

Syntax

TRUNCATE TABLE table_name;

MySQL ALTER TABLE Statement

The ALTER TABLE statement is used to add, delete, or modify columns in an existing table.

The ALTER TABLE statement is also used to add and drop various constraints on an existing table.

ALTER TABLE - ADD Column

To add a column in a table, use the following syntax:

ALTER TABLE table_name
ADD column_name datatype;

The following SQL adds an "Email" column to the "Customers" table:

Example

ALTER TABLE Customers
ADD Email varchar(255);

ALTER TABLE - DROP COLUMN

To delete a column in a table, use the following syntax (notice that some database systems don't allow deleting a column):

ALTER TABLE table_name
DROP COLUMN column_name;

The following SQL deletes the "Email" column from the "Customers" table:

Example

ALTER TABLE Customers
DROP COLUMN Email;

ALTER TABLE - MODIFY COLUMN

To change the data type of a column in a table, use the following syntax:

ALTER TABLE table_name
MODIFY COLUMN column_name datatype;

MySQL Constraints

SQL constraints are used to specify rules for data in a table.

Create Constraints

Constraints can be specified when the table is created with the CREATE TABLE statement, or after the table is created with the ALTER TABLE statement.

Syntax

CREATE TABLE table_name (
column1 datatype constraint,
column2 datatype constraint,
column3 datatype constraint,
....
);

MySQL Constraints

SQL constraints are used to specify rules for the data in a table.

Constraints are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the table. If there is any violation between the constraint and the data action, the action is aborted.

Constraints can be column level or table level. Column level constraints apply to a column, and table level constraints apply to the whole table.

The following constraints are commonly used in SQL:

  • NOT NULL - Ensures that a column cannot have a NULL value
  • UNIQUE - Ensures that all values in a column are different
  • PRIMARY KEY - A combination of a NOT NULL and UNIQUE. Uniquely identifies each row in a table
  • FOREIGN KEY - Prevents actions that would destroy links between tables
  • CHECK - Ensures that the values in a column satisfy a specific condition
  • DEFAULT - Sets a default value for a column if no value is specified
  • CREATE INDEX - Used to create and retrieve data from the database very quickly

NOT NULL on CREATE TABLE

The following SQL ensures that the "ID", "LastName", and "FirstName" columns will NOT accept NULL values when the "Persons" table is created:

CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255) NOT NULL,
Age int
);

NOT NULL on ALTER TABLE

To create a NOT NULL constraint on the "Age" column when the "Persons" table is already created, use the following SQL:

ALTER TABLE Persons
MODIFY Age int NOT NULL;

MySQL UNIQUE Constraint

The UNIQUE constraint ensures that all values in a column are different.

Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns.

A PRIMARY KEY constraint automatically has a UNIQUE constraint.

However, you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table.

UNIQUE Constraint on CREATE TABLE

The following SQL creates a UNIQUE constraint on the "ID" column when the "Persons" table is created:

CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
UNIQUE (ID)
);

To name a UNIQUE constraint, and to define a UNIQUE constraint on multiple columns, use the following SQL syntax:

CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
CONSTRAINT UC_Person UNIQUE (ID,LastName)
);

UNIQUE Constraint on ALTER TABLE

To create a UNIQUE constraint on the "ID" column when the table is already created, use the following SQL:

ALTER TABLE Persons
ADD UNIQUE (ID);

To name a UNIQUE constraint, and to define a UNIQUE constraint on multiple columns, use the following SQL syntax:

ALTER TABLE Persons
ADD CONSTRAINT UC_Person UNIQUE (ID,LastName);

DROP a UNIQUE Constraint

To drop a UNIQUE constraint, use the following SQL:

ALTER TABLE Persons
DROP INDEX UC_Person;

PRIMARY KEY on CREATE TABLE

The following SQL creates a PRIMARY KEY on the "ID" column when the "Persons" table is created:

CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
PRIMARY KEY (ID)
);

To allow naming of a PRIMARY KEY constraint, and for defining a PRIMARY KEY constraint on multiple columns, use the following SQL syntax:

CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
CONSTRAINT PK_Person PRIMARY KEY (ID,LastName)
);

Note: In the example above there is only ONE PRIMARY KEY (PK_Person). However, the VALUE of the primary key is made up of TWO COLUMNS (ID + LastName).

PRIMARY KEY on ALTER TABLE

To create a PRIMARY KEY constraint on the "ID" column when the table is already created, use the following SQL:

ALTER TABLE Persons
ADD PRIMARY KEY (ID);

To allow naming of a PRIMARY KEY constraint, and for defining a PRIMARY KEY constraint on multiple columns, use the following SQL syntax:

ALTER TABLE Persons
ADD CONSTRAINT PK_Person PRIMARY KEY (ID,LastName);

Note: If you use ALTER TABLE to add a primary key, the primary key column(s) must have been declared to not contain NULL values (when the table was first created).

DROP a PRIMARY KEY Constraint

To drop a PRIMARY KEY constraint, use the following SQL:

ALTER TABLE Persons
DROP PRIMARY KEY;

MySQL FOREIGN KEY Constraint

The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables.

A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table.

The table with the foreign key is called the child table, and the table with the primary key is called the referenced or parent table.

Look at the following two tables:

Persons Table

PersonID LastName FirstName Age
1 Hansen Ola 30
2 Svendson Tove 23
3 Pettersen Kari 20

Orders Table

OrderID OrderNumber PersonID
1 77895 3
2 44678 3
3 22456 2
4 24562 1

Notice that the "PersonID" column in the "Orders" table points to the "PersonID" column in the "Persons" table.

The "PersonID" column in the "Persons" table is the PRIMARY KEY in the "Persons" table.

The "PersonID" column in the "Orders" table is a FOREIGN KEY in the "Orders" table.

The FOREIGN KEY constraint prevents invalid data from being inserted into the foreign key column, because it has to be one of the values contained in the parent table.

FOREIGN KEY on CREATE TABLE

The following SQL creates a FOREIGN KEY on the "PersonID" column when the "Orders" table is created:

CREATE TABLE Orders (
OrderID int NOT NULL,
OrderNumber int NOT NULL,
PersonID int,
PRIMARY KEY (OrderID),
FOREIGN KEY (PersonID) REFERENCES Persons(PersonID)
);

To allow naming of a FOREIGN KEY constraint, and for defining a FOREIGN KEY constraint on multiple columns, use the following SQL syntax:

CREATE TABLE Orders (
OrderID int NOT NULL,
OrderNumber int NOT NULL,
PersonID int,
PRIMARY KEY (OrderID),
CONSTRAINT FK_PersonOrder FOREIGN KEY (PersonID)
REFERENCES Persons(PersonID)
);

FOREIGN KEY on ALTER TABLE

To create a FOREIGN KEY constraint on the "PersonID" column when the "Orders" table is already created, use the following SQL:

ALTER TABLE Orders
ADD FOREIGN KEY (PersonID) REFERENCES Persons(PersonID);

To allow naming of a FOREIGN KEY constraint, and for defining a FOREIGN KEY constraint on multiple columns, use the following SQL syntax:

ALTER TABLE Orders
ADD CONSTRAINT FK_PersonOrder
FOREIGN KEY (PersonID) REFERENCES Persons(PersonID);

DROP a FOREIGN KEY Constraint

To drop a FOREIGN KEY constraint, use the following SQL:

ALTER TABLE Orders
DROP FOREIGN KEY FK_PersonOrder;

MySQL CHECK Constraint

The CHECK constraint is used to limit the value range that can be placed in a column.

If you define a CHECK constraint on a column it will allow only certain values for this column.

If you define a CHECK constraint on a table it can limit the values in certain columns based on values in other columns in the row.

CHECK on CREATE TABLE

The following SQL creates a CHECK constraint on the "Age" column when the "Persons" table is created. The CHECK constraint ensures that the age of a person must be 18, or older:

CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
CHECK (Age >= 18)
);

To allow naming of a CHECK constraint, and for defining a CHECK constraint on multiple columns, use the following SQL syntax:

CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
City varchar(255),
CONSTRAINT CHK_Person CHECK (Age >= 18 AND City='Sandnes')
);

CHECK on ALTER TABLE

To create a CHECK constraint on the "Age" column when the table is already created, use the following SQL:

ALTER TABLE Persons
ADD CHECK (Age >= 18);

To allow naming of a CHECK constraint, and for defining a CHECK constraint on multiple columns, use the following SQL syntax:

ALTER TABLE Persons
ADD CONSTRAINT CHK_PersonAge CHECK (Age >= 18 AND City='Sandnes');

DROP a CHECK Constraint

To drop a CHECK constraint, use the following SQL:

ALTER TABLE Persons
DROP CHECK CHK_PersonAge;

MySQL DEFAULT Constraint

The DEFAULT constraint is used to set a default value for a column.

The default value will be added to all new records, if no other value is specified.

DEFAULT on CREATE TABLE

The following SQL sets a DEFAULT value for the "City" column when the "Persons" table is created:

CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),< Age int,
City varchar(255) DEFAULT 'Sandnes'
);

The DEFAULT constraint can also be used to insert system values, by using functions like CURRENT_DATE():

CREATE TABLE Orders (
ID int NOT NULL,
OrderNumber int NOT NULL,
OrderDate date DEFAULT CURRENT_DATE()
);

DEFAULT on ALTER TABLE

To create a DEFAULT constraint on the "City" column when the table is already created, use the following SQL:

ALTER TABLE Persons
ALTER City SET DEFAULT 'Sandnes';

DROP a DEFAULT Constraint

To drop a DEFAULT constraint, use the following SQL:

ALTER TABLE Persons
ALTER City DROP DEFAULT;

MySQL CREATE INDEX Statement

The CREATE INDEX statement is used to create indexes in tables.

Indexes are used to retrieve data from the database more quickly than otherwise. The users cannot see the indexes, they are just used to speed up searches/queries.

CREATE INDEX Syntax

Creates an index on a table. Duplicate values are allowed:

CREATE INDEX index_name
ON table_name (column1, column2, ...);

CREATE UNIQUE INDEX Syntax

Creates a unique index on a table. Duplicate values are not allowed:

CREATE UNIQUE INDEX index_name
ON table_name (column1, column2, ...);

MySQL CREATE INDEX Example

The SQL statement below creates an index named "idx_lastname" on the "LastName" column in the "Persons" table:

CREATE INDEX idx_lastname
ON Persons (LastName);

If you want to create an index on a combination of columns, you can list the column names within the parentheses, separated by commas:

CREATE INDEX idx_pname
ON Persons (LastName, FirstName);

DROP INDEX Statement

The DROP INDEX statement is used to delete an index in a table.

ALTER TABLE table_name
DROP INDEX index_name;

MySQL AUTO INCREMENT Field

What is an AUTO INCREMENT Field?

Auto-increment allows a unique number to be generated automatically when a new record is inserted into a table.

Often this is the primary key field that we would like to be created automatically every time a new record is inserted.

MySQL AUTO_INCREMENT Keyword

MySQL uses the AUTO_INCREMENT keyword to perform an auto-increment feature.

By default, the starting value for AUTO_INCREMENT is 1, and it will increment by 1 for each new record.

The following SQL statement defines the "Personid" column to be an auto-increment primary key field in the "Persons" table:

CREATE TABLE Persons (
Personid int NOT NULL AUTO_INCREMENT,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
PRIMARY KEY (Personid)
);

To let the AUTO_INCREMENT sequence start with another value, use the following SQL statement:

ALTER TABLE Persons AUTO_INCREMENT=100;

When we insert a new record into the "Persons" table, we do NOT have to specify a value for the "Personid" column (a unique value will be added automatically):

INSERT INTO Persons (FirstName,LastName)
VALUES ('Lars','Monsen');

The SQL statement above would insert a new record into the "Persons" table. The "Personid" column would be assigned a unique value automatically. The "FirstName" column would be set to "Lars" and the "LastName" column would be set to "Monsen".

MySQL Working With Dates

MySQL Dates

As long as your data contains only the date portion, your queries will work as expected. However, if a time portion is involved, it gets more complicated.

MySQL Date Data Types

MySQL comes with the following data types for storing a date or a date/time value in the database:

  • DATE - format YYYY-MM-DD
  • DATETIME - format: YYYY-MM-DD HH:MI:SS
  • TIMESTAMP - format: YYYY-MM-DD HH:MI:SS
  • YEAR - format YYYY or YY

Note: The date data type are set for a column when you create a new table in your database!

Working with Dates

Look at the following table:

Orders Table

OrderId ProductName OrderDate
1 Geitost 2008-11-11
2 Camembert Pierrot 2008-11-09
3 Mozzarella di Giovanni 2008-11-11
4 Mascarpone Fabioli 2008-10-29

Now we want to select the records with an OrderDate of "2008-11-11" from the table above.

We use the following SELECT statement:

SELECT * FROM Orders WHERE OrderDate='2008-11-11'

The result-set will look like this:

OrderId ProductName OrderDate
1 Geitost 2008-11-11
3 Mozzarella di Giovanni 2008-11-11

Note: Two dates can easily be compared if there is no time component involved!

Now, assume that the "Orders" table looks like this (notice the added time-component in the "OrderDate" column):

OrderId ProductName OrderDate
1 Geitost 2008-11-11 13:23:44
2 Camembert Pierrot 2008-11-09 15:45:21
3 Mozzarella di Giovanni 2008-11-11 11:12:01
4 Mascarpone Fabioli 2008-10-29 14:56:59

If we use the same SELECT statement as above:

SELECT * FROM Orders WHERE OrderDate='2008-11-11'

we will get no result! This is because the query is looking only for dates with no time portion.

Tip: To keep your queries simple and easy to maintain, do not use time-components in your dates, unless you have to!

MySQL Views

MySQL CREATE VIEW Statement

In SQL, a view is a virtual table based on the result-set of an SQL statement.

A view contains rows and columns, just like a real table. The fields in a view are fields from one or more real tables in the database.

You can add SQL statements and functions to a view and present the data as if the data were coming from one single table.

A view is created with the CREATE VIEW statement.

CREATE VIEW Syntax

CREATE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

Note: A view always shows up-to-date data! The database engine recreates the view, every time a user queries it.

MySQL CREATE VIEW Examples

The following SQL creates a view that shows all customers from Brazil:

Example

CREATE VIEW [Brazil Customers] AS
SELECT CustomerName, ContactName
FROM Customers
WHERE Country = 'Brazil';

We can query the view above as follows:

Example

SELECT * FROM [Brazil Customers];

The following SQL creates a view that selects every product in the "Products" table with a price higher than the average price:

Example

CREATE VIEW [Products Above Average Price] AS
SELECT ProductName, Price
FROM Products
WHERE Price > (SELECT AVG(Price) FROM Products);

We can query the view above as follows:

Example

SELECT * FROM [Products Above Average Price];

MySQL Updating a View

A view can be updated with the CREATE OR REPLACE VIEW statement.

CREATE OR REPLACE VIEW Syntax

CREATE OR REPLACE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

The following SQL adds the "City" column to the "Brazil Customers" view:

Example

CREATE OR REPLACE VIEW [Brazil Customers] AS
SELECT CustomerName, ContactName, City
FROM Customers
WHERE Country = 'Brazil';

MySQL Dropping a View

A view is deleted with the DROP VIEW statement.

DROP VIEW Syntax

DROP VIEW view_name;

The following SQL drops the "Brazil Customers" view:

Example

DROP VIEW [Brazil Customers];

MySQL Data Types

MySQL Data Types (Version 8.0)

Each column in a database table is required to have a name and a data type.

An SQL developer must decide what type of data that will be stored inside each column when creating a table. The data type is a guideline for SQL to understand what type of data is expected inside of each column, and it also identifies how SQL will interact with the stored data.

In MySQL there are three main data types: string, numeric, and date and time.

String Data Types

Data type Description
CHAR(size) A FIXED length string (can contain letters, numbers, and special characters). The size parameter specifies the column length in characters - can be from 0 to 255. Default is 1
VARCHAR(size) A VARIABLE length string (can contain letters, numbers, and special characters). The size parameter specifies the maximum column length in characters - can be from 0 to 65535
BINARY(size) Equal to CHAR(), but stores binary byte strings. The size parameter specifies the column length in bytes. Default is 1
VARBINARY(size) Equal to VARCHAR(), but stores binary byte strings. The size parameter specifies the maximum column length in bytes.
TINYBLOB For BLOBs (Binary Large OBjects). Max length: 255 bytes
TINYTEXT Holds a string with a maximum length of 255 characters
TEXT(size) Holds a string with a maximum length of 65,535 bytes
BLOB(size) For BLOBs (Binary Large OBjects). Holds up to 65,535 bytes of data
MEDIUMTEXT Holds a string with a maximum length of 16,777,215 characters
MEDIUMBLOB For BLOBs (Binary Large OBjects). Holds up to 16,777,215 bytes of data
LONGTEXT Holds a string with a maximum length of 4,294,967,295 characters
LONGBLOB For BLOBs (Binary Large OBjects). Holds up to 4,294,967,295 bytes of data
ENUM(val1, val2, val3, ...) A string object that can have only one value, chosen from a list of possible values. You can list up to 65535 values in an ENUM list. If a value is inserted that is not in the list, a blank value will be inserted. The values are sorted in the order you enter them
SET(val1, val2, val3, ...) A string object that can have 0 or more values, chosen from a list of possible values. You can list up to 64 values in a SET list

Numeric Data Types

Data type Description
BIT(size) A bit-value type. The number of bits per value is specified in size. The size parameter can hold a value from 1 to 64. The default value for size is 1.
TINYINT(size) A very small integer. Signed range is from -128 to 127. Unsigned range is from 0 to 255. The size parameter specifies the maximum display width (which is 255)
BOOL Zero is considered as false, nonzero values are considered as true.
BOOLEAN Equal to BOOL
SMALLINT(size) A small integer. Signed range is from -32768 to 32767. Unsigned range is from 0 to 65535. The size parameter specifies the maximum display width (which is 255)
MEDIUMINT(size) A medium integer. Signed range is from -8388608 to 8388607. Unsigned range is from 0 to 16777215. The size parameter specifies the maximum display width (which is 255)
INT(size) A medium integer. Signed range is from -2147483648 to 2147483647. Unsigned range is from 0 to 4294967295. The size parameter specifies the maximum display width (which is 255)
INTEGER(size) Equal to INT(size)
BIGINT(size) A large integer. Signed range is from -9223372036854775808 to 9223372036854775807. Unsigned range is from 0 to 18446744073709551615. The size parameter specifies the maximum display width (which is 255)
FLOAT(size, d) A floating point number. The total number of digits is specified in size. The number of digits after the decimal point is specified in the d parameter. This syntax is deprecated in MySQL 8.0.17, and it will be removed in future MySQL versions
FLOAT(p) A floating point number. MySQL uses the p value to determine whether to use FLOAT or DOUBLE for the resulting data type. If p is from 0 to 24, the data type becomes FLOAT(). If p is from 25 to 53, the data type becomes DOUBLE()
DOUBLE(size, d) A normal-size floating point number. The total number of digits is specified in size. The number of digits after the decimal point is specified in the d parameter
DOUBLE PRECISION(size, d)
DECIMAL(size, d) An exact fixed-point number. The total number of digits is specified in size. The number of digits after the decimal point is specified in the d parameter. The maximum number for size is 65. The maximum number for d is 30. The default value for size is 10. The default value for d is 0.
DEC(size, d) Equal to DECIMAL(size,d)

Note: All the numeric data types may have an extra option: UNSIGNED or ZEROFILL. If you add the UNSIGNED option, MySQL disallows negative values for the column. If you add the ZEROFILL option, MySQL automatically also adds the UNSIGNED attribute to the column.

Date and Time Data Types

Data type Description
DATE A date. Format: YYYY-MM-DD. The supported range is from '1000-01-01' to '9999-12-31'
DATETIME(fsp) A date and time combination. Format: YYYY-MM-DD hh:mm:ss. The supported range is from '1000-01-01 00:00:00' to '9999-12-31 23:59:59'. Adding DEFAULT and ON UPDATE in the column definition to get automatic initialization and updating to the current date and time
TIMESTAMP(fsp) A timestamp. TIMESTAMP values are stored as the number of seconds since the Unix epoch ('1970-01-01 00:00:00' UTC). Format: YYYY-MM-DD hh:mm:ss. The supported range is from '1970-01-01 00:00:01' UTC to '2038-01-09 03:14:07' UTC. Automatic initialization and updating to the current date and time can be specified using DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP in the column definition
TIME(fsp) A time. Format: hh:mm:ss. The supported range is from '-838:59:59' to '838:59:59'
YEAR A year in four-digit format. Values allowed in four-digit format: 1901 to 2155, and 0000.
MySQL 8.0 does not support year in two-digit format.

MySQL Functions

MySQL has many built-in functions.

This reference contains string, numeric, date, and some advanced functions in MySQL.

MySQL String Functions

Function Description
ASCII Returns the ASCII value for the specific character
CHAR_LENGTH Returns the length of a string (in characters)
CHARACTER_LENGTH Returns the length of a string (in characters)
CONCAT Adds two or more expressions together
CONCAT_WS Adds two or more expressions together with a separator
FIELD Returns the index position of a value in a list of values
FIND_IN_SET Returns the position of a string within a list of strings
FORMAT Formats a number to a format like "#,###,###.##", rounded to a specified number of decimal places
INSERT Inserts a string within a string at the specified position and for a certain number of characters
INSTR Returns the position of the first occurrence of a string in another string
LCASE Converts a string to lower-case
LEFT Extracts a number of characters from a string (starting from left)
LENGTH Returns the length of a string (in bytes)
LOCATE Returns the position of the first occurrence of a substring in a string
LOWER Converts a string to lower-case
LPAD Left-pads a string with another string, to a certain length
LTRIM Removes leading spaces from a string
MID Extracts a substring from a string (starting at any position)
POSITION Returns the position of the first occurrence of a substring in a string
REPEAT Repeats a string as many times as specified
REPLACE Replaces all occurrences of a substring within a string, with a new substring
REVERSE Reverses a string and returns the result
RIGHT Extracts a number of characters from a string (starting from right)
RPAD Right-pads a string with another string, to a certain length
RTRIM Removes trailing spaces from a string
SPACE Returns a string of the specified number of space characters
STRCMP Compares two strings
SUBSTR Extracts a substring from a string (starting at any position)
SUBSTRING Extracts a substring from a string (starting at any position)
SUBSTRING_INDEX Returns a substring of a string before a specified number of delimiter occurs
TRIM Removes leading and trailing spaces from a string
UCASE Converts a string to upper-case
UPPER Converts a string to upper-case

MySQL Numeric Functions

Function Description
ABS Returns the absolute value of a number
ACOS Returns the arc cosine of a number
ASIN Returns the arc sine of a number
ATAN Returns the arc tangent of one or two numbers
ATAN2 Returns the arc tangent of two numbers
AVG Returns the average value of an expression
CEIL Returns the smallest integer value that is >= to a number
CEILING Returns the smallest integer value that is >= to a number
COS Returns the cosine of a number
COT Returns the cotangent of a number
COUNT Returns the number of records returned by a select query
DEGREES Converts a value in radians to degrees
DIV Used for integer division
EXP Returns e raised to the power of a specified number
FLOOR Returns the largest integer value that is <= to a number
GREATEST Returns the greatest value of the list of arguments
LEAST Returns the smallest value of the list of arguments
LN Returns the natural logarithm of a number
LOG Returns the natural logarithm of a number, or the logarithm of a number to a specified base
LOG10 Returns the natural logarithm of a number to base 10
LOG2 Returns the natural logarithm of a number to base 2
MAX Returns the maximum value in a set of values
MIN Returns the minimum value in a set of values
MOD Returns the remainder of a number divided by another number
PI Returns the value of PI
POW Returns the value of a number raised to the power of another number
POWER Returns the value of a number raised to the power of another number
RADIANS Converts a degree value into radians
RAND Returns a random number
ROUND Rounds a number to a specified number of decimal places
SIGN Returns the sign of a number
SIN Returns the sine of a number
SQRT Returns the square root of a number
SUM Calculates the sum of a set of values
TAN Returns the tangent of a number
TRUNCATE Truncates a number to the specified number of decimal places

MySQL Date Functions

Function Description
ADDDATE Adds a time/date interval to a date and then returns the date
ADDTIME Adds a time interval to a time/datetime and then returns the time/datetime
CURDATE Returns the current date
CURRENT_DATE Returns the current date
CURRENT_TIME Returns the current time
CURRENT_TIMESTAMP Returns the current date and time
CURTIME Returns the current time
DATE Extracts the date part from a datetime expression
DATEDIFF Returns the number of days between two date values
DATE_ADD Adds a time/date interval to a date and then returns the date
DATE_FORMAT Formats a date
DATE_SUB Subtracts a time/date interval from a date and then returns the date
DAY Returns the day of the month for a given date
DAYNAME Returns the weekday name for a given date
DAYOFMONTH Returns the day of the month for a given date
DAYOFWEEK Returns the weekday index for a given date
DAYOFYEAR Returns the day of the year for a given date
EXTRACT Extracts a part from a given date
FROM_DAYS Returns a date from a numeric datevalue
HOUR Returns the hour part for a given date
LAST_DAY Extracts the last day of the month for a given date
LOCALTIME Returns the current date and time
LOCALTIMESTAMP Returns the current date and time
MAKEDATE Creates and returns a date based on a year and a number of days value
MAKETIME Creates and returns a time based on an hour, minute, and second value
MICROSECOND Returns the microsecond part of a time/datetime
MINUTE Returns the minute part of a time/datetime
MONTH Returns the month part for a given date
MONTHNAME Returns the name of the month for a given date
NOW Returns the current date and time
PERIOD_ADD Adds a specified number of months to a period
PERIOD_DIFF Returns the difference between two periods
QUARTER Returns the quarter of the year for a given date value
SECOND Returns the seconds part of a time/datetime
SEC_TO_TIME Returns a time value based on the specified seconds
STR_TO_DATE Returns a date based on a string and a format
SUBDATE Subtracts a time/date interval from a date and then returns the date
SUBTIME Subtracts a time interval from a datetime and then returns the time/datetime
SYSDATE Returns the current date and time
TIME Extracts the time part from a given time/datetime
TIME_FORMAT Formats a time by a specified format
TIME_TO_SEC Converts a time value into seconds
TIMEDIFF Returns the difference between two time/datetime expressions
TIMESTAMP Returns a datetime value based on a date or datetime value
TO_DAYS Returns the number of days between a date and date "0000-00-00"
WEEK Returns the week number for a given date
WEEKDAY Returns the weekday number for a given date
WEEKOFYEAR Returns the week number for a given date
YEAR Returns the year part for a given date
YEARWEEK Returns the year and week number for a given date

MySQL Advanced Functions

Function Description
BIN Returns a binary representation of a number
BINARY Converts a value to a binary string
CASE Goes through conditions and return a value when the first condition is met
CAST Converts a value (of any type) into a specified datatype
COALESCE Returns the first non-null value in a list
CONNECTION_ID Returns the unique connection ID for the current connection
CONV Converts a number from one numeric base system to another
CONVERT Converts a value into the specified datatype or character set
CURRENT_USER Returns the user name and host name for the MySQL account that the server used to authenticate the current client
DATABASE Returns the name of the current database
IF Returns a value if a condition is TRUE, or another value if a condition is FALSE
IFNULL Return a specified value if the expression is NULL, otherwise return the expression
ISNULL Returns 1 or 0 depending on whether an expression is NULL
LAST_INSERT_ID Returns the AUTO_INCREMENT id of the last row that has been inserted or updated in a table
NULLIF Compares two expressions and returns NULL if they are equal. Otherwise, the first expression is returned
SESSION_USER Returns the current MySQL user name and host name
SYSTEM_USER Returns the current MySQL user name and host name
USER Returns the current MySQL user name and host name
VERSION Returns the current version of the MySQL database

The MySQL SELECT Statement

The SELECT statement is used to select data from a database.

The data returned is stored in a result table, called the result-set.

SELECT Syntax

SELECT column1, column2, ...
FROM table_name;

Here, column1, column2, ... are the field names of the table you want to select data from. If you want to select all the fields available in the table, use the following syntax:

SELECT * FROM table_name;

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the "Customers" table in the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
1

 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4

 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK
5 Berglunds snabbköp Christina Berglund Berguvsvägen 8 Luleå S-958 22 Sweden

SELECT Columns Example

The following SQL statement selects the "CustomerName", "City", and "Country" columns from the "Customers" table:

Example

SELECT CustomerName, City, Country FROM Customers;

SELECT * Example

The following SQL statement selects ALL the columns from the "Customers" table:

Example

SELECT * FROM Customers;

The MySQL SELECT DISTINCT Statement

The SELECT DISTINCT statement is used to return only distinct (different) values.

Inside a table, a column often contains many duplicate values; and sometimes you only want to list the different (distinct) values.

SELECT DISTINCT Syntax

SELECT DISTINCT column1, column2, ...
FROM table_name;

SELECT Example Without DISTINCT

The following SQL statement selects all (including the duplicates) values from the "Country" column in the "Customers" table:

Example

SELECT Country FROM Customers;

SELECT DISTINCT Examples

The following SQL statement selects only the DISTINCT values from the "Country" column in the "Customers" table:

Example

SELECT DISTINCT Country FROM Customers;

The following SQL statement counts and returns the number of different (distinct) countries in the "Customers" table:

Example

SELECT COUNT(DISTINCT Country) FROM Customers;

The MySQL WHERE Clause

The WHERE clause is used to filter records.

It is used to extract only those records that fulfill a specified condition.

WHERE Syntax

SELECT column1, column2, ...
FROM table_name
WHERE condition;

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK
5 Berglunds snabbköp Christina Berglund Berguvsvägen 8 Luleå S-958 22 Sweden

WHERE Clause Example

The following SQL statement selects all the customers from "Mexico":

SELECT * FROM Customers WHERE Country = 'Mexico';

Text Fields vs. Numeric Fields

SQL requires single quotes around text values (most database systems will also allow double quotes).

However, numeric fields should not be enclosed in quotes:

SELECT * FROM Customers WHERE CustomerID = 1;

Operators in The WHERE Clause

The following operators can be used in the WHERE clause:

Operator Description Example
= Equal Try it
> Greater than Try it
< Less than Try it
>= Greater than or equal Try it
<= Less than or equal Try it
<> Not equal. Note: In some versions of SQL this operator may be written as != Try it
BETWEEN Between a certain range Try it
LIKE Search for a pattern Try it
IN To specify multiple possible values for a column Try it

The MySQL WHERE Clause

The WHERE clause can be combined with AND, OR, and NOT operators.

The AND and OR operators are used to filter records based on more than one condition:

  • The AND operator displays a record if all the conditions separated by AND are TRUE.
  • The OR operator displays a record if any of the conditions separated by OR is TRUE.

The NOT operator displays a record if the condition(s) is NOT TRUE.

AND Syntax

SELECT column1, column2, ...
FROM table_name
WHERE condition1 AND condition2 AND condition3 ...;

OR Syntax

SELECT column1, column2, ...
FROM table_name
WHERE condition1 OR condition2 OR condition3 ...;

NOT Syntax

SELECT column1, column2, ...
FROM table_name
WHERE NOT condition;

AND Example

The following SQL statement selects all fields from "Customers" where country is "Germany" AND city is "Berlin":

SELECT * FROM Customers
WHERE Country = 'Germany' AND City = 'Berlin';

OR Example

The following SQL statement selects all fields from "Customers" where city is "Berlin" OR "Stuttgart":

SELECT * FROM Customers
WHERE City = 'Berlin' OR City = 'Stuttgart';

The following SQL statement selects all fields from "Customers" where country is "Germany" OR "Spain":

SELECT * FROM Customers
WHERE Country = 'Germany' OR Country = 'Spain';

NOT Example

The following SQL statement selects all fields from "Customers" where country is NOT "Germany":

SELECT * FROM Customers
WHERE NOT Country = 'Germany';

Combining AND, OR and NOT

You can also combine the AND, OR, and NOT operators.

The following SQL statement selects all fields from "Customers" where country is "Germany" AND city must be "Berlin" OR "Stuttgart" (use parenthesis to form complex expressions):

SELECT * FROM Customers
WHERE Country = 'Germany' AND (City = 'Berlin' OR City = 'Stuttgart');

The following SQL statement selects all fields from "Customers" where country is NOT "Germany" and NOT "USA":

SELECT * FROM Customers
WHERE NOT Country = 'Germany' AND NOT Country = 'USA';

MySQL ORDER BY Keyword

The MySQL ORDER BY Keyword

The ORDER BY keyword is used to sort the result-set in ascending or descending order.

The ORDER BY keyword sorts the records in ascending order by default. To sort the records in descending order, use the DESC keyword.

ORDER BY Syntax

SELECT column1, column2, ...
FROM table_name
ORDER BY column1, column2, ... ASC|DESC;

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK
5 Berglunds snabbköp Christina Berglund Berguvsvägen 8 Luleå S-958 22 Sweden

ORDER BY Example

The following SQL statement selects all customers from the "Customers" table, sorted by the "Country" column:

SELECT * FROM Customers
ORDER BY Country;

ORDER BY DESC Example

The following SQL statement selects all customers from the "Customers" table, sorted DESCENDING by the "Country" column:

Example

SELECT * FROM Customers
ORDER BY Country DESC;

ORDER BY Several Columns Example

The following SQL statement selects all customers from the "Customers" table, sorted by the "Country" and the "CustomerName" column. This means that it orders by Country, but if some rows have the same Country, it orders them by CustomerName:

Example

SELECT * FROM Customers
ORDER BY Country, CustomerName;

ORDER BY Several Columns Example 2

The following SQL statement selects all customers from the "Customers" table, sorted ascending by the "Country" and descending by the "CustomerName" column:

Example

SELECT * FROM Customers
ORDER BY Country ASC, CustomerName DESC;

The MySQL INSERT INTO Statement

The INSERT INTO statement is used to insert new records in a table.

INSERT INTO Syntax

It is possible to write the INSERT INTO statement in two ways:

  1. Specify both the column names and the values to be inserted:
    2. INSERT INTO table_name (column1, column2, column3, ...)
    VALUES (value1, value2, value3, ...);
  2. If you are adding values for all the columns of the table, you do not need to specify the column names in the SQL query. However, make sure the order of the values is in the same order as the columns in the table.
    3. INSERT INTO table_name
    VALUES (value1, value2, value3, ...);

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
89 White Clover Markets Karl Jablonski 305 - 14th Ave. S. Suite 3B Seattle 98128 USA
90 Wilman Kala Matti Karttunen Keskuskatu 45 Helsinki 21240 Finland
91 Wolski Zbyszek ul. Filtrowa 68 Walla 01-012 Poland

INSERT INTO Example

The following SQL statement inserts a new record in the "Customers" table:

INSERT INTO Customers (CustomerName, ContactName, Address, City, PostalCode, Country)
VALUES ('Cardinal', 'Tom B. Erichsen', 'Skagen 21', 'Stavanger', '4006', 'Norway');

The selection from the "Customers" table will now look like this:

CustomerID CustomerName ContactName Address City PostalCode Country
89 White Clover Markets Karl Jablonski 305 - 14th Ave. S. Suite 3B Seattle 98128 USA
90 Wilman Kala Matti Karttunen Keskuskatu 45 Helsinki 21240 Finland
91 Wolski Zbyszek ul. Filtrowa 68 Walla 01-012 Poland
92 Cardinal Tom B. Erichsen Skagen 21 Stavanger 4006 Norway

Did you notice that we did not insert any number into the CustomerID field?
The CustomerID column is an auto-increment field and will be generated automatically when a new record is inserted into the table.

Insert Data Only in Specified Columns

It is also possible to only insert data in specific columns.

The following SQL statement will insert a new record, but only insert data in the "CustomerName", "City", and "Country" columns (CustomerID will be updated automatically):

INSERT INTO Customers (CustomerName, City, Country)
VALUES ('Cardinal', 'Stavanger', 'Norway');

The selection from the "Customers" table will now look like this:

CustomerID CustomerName ContactName Address City PostalCode Country
89 White Clover Markets Karl Jablonski 305 - 14th Ave. S. Suite 3B Seattle 98128 USA
90 Wilman Kala Matti Karttunen Keskuskatu 45 Helsinki 21240 Finland
91 Wolski Zbyszek ul. Filtrowa 68 Walla 01-012 Poland
92 Cardinal null null Stavanger null Norway
93 Cardinal null null Stavanger null Norway

MySQL NULL Values

What is a NULL Value?

A field with a NULL value is a field with no value.

If a field in a table is optional, it is possible to insert a new record or update a record without adding a value to this field. Then, the field will be saved with a NULL value.

Note: A NULL value is different from a zero value or a field that contains spaces. A field with a NULL value is one that has been left blank during record creation!

How to Test for NULL Values?

It is not possible to test for NULL values with comparison operators, such as =, <, or <>.

We will have to use the IS NULL and IS NOT NULL operators instead.

IS NULL Syntax

SELECT column_names
FROM table_name
WHERE column_name IS NULL;

IS NOT NULL Syntax

SELECT column_names
FROM table_name
WHERE column_name IS NOT NULL;

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK
5 Berglunds snabbköp Christina Berglund Berguvsvägen 8 Luleå S-958 22 Sweden

The IS NULL Operator

The IS NULL operator is used to test for empty values (NULL values).

The following SQL lists all customers with a NULL value in the "Address" field:

Example

SELECT CustomerName, ContactName, Address
FROM Customers
WHERE Address IS NULL;

The IS NOT NULL Operator

The IS NOT NULL operator is used to test for non-empty values (NOT NULL values).

The following SQL lists all customers with a value in the "Address" field:

Example

SELECT CustomerName, ContactName, Address
FROM Customers
WHERE Address IS NOT NULL;

MySQL UPDATE Statement

The MySQL UPDATE Statement

The UPDATE statement is used to modify the existing records in a table.

UPDATE Syntax

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

Note: Be careful when updating records in a table! Notice the WHERE clause in the UPDATE statement. The WHERE clause specifies which record(s) that should be updated. If you omit the WHERE clause, all records in the table will be updated!

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK

UPDATE Table

The following SQL statement updates the first customer (CustomerID = 1) with a new contact person and a new city.

Example

UPDATE Customers
SET ContactName = 'Alfred Schmidt', City = 'Frankfurt'
WHERE CustomerID = 1;

The selection from the "Customers" table will now look like this:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Alfred Schmidt Obere Str. 57 Frankfurt 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK

UPDATE Multiple Records

It is the WHERE clause that determines how many records will be updated.

Example

UPDATE Customers
SET PostalCode = 00000
WHERE Country = 'Mexico';

The selection from the "Customers" table will now look like this:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Alfred Schmidt Obere Str. 57 Frankfurt 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 00000 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 00000 Mexico
4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK

Update Warning!

Be careful when updating records. If you omit the WHERE clause, ALL records will be updated!

Example

UPDATE Customers
SET PostalCode = 00000;

The selection from the "Customers" table will now look like this:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Alfred Schmidt Obere Str. 57 Frankfurt 00000 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 00000 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 00000 Mexico
4

 Around the Horn Thomas Hardy 120 Hanover Sq. London 00000 UK

MySQL DELETE Statement

The DELETE statement is used to delete existing records in a table.

DELETE Syntax

DELETE FROM table_name WHERE condition;

Note: Be careful when deleting records in a table! Notice the WHERE clause in the DELETE statement. The WHERE clause specifies which record(s) should be deleted. If you omit the WHERE clause, all records in the table will be deleted!

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany

SQL DELETE Example

The following SQL statement deletes the customer "Alfreds Futterkiste" from the "Customers" table:

Example

DELETE FROM Customers WHERE CustomerName='Alfreds Futterkiste';

The "Customers" table will now look like this:

Delete All Records

It is possible to delete all rows in a table without deleting the table. This means that the table structure, attributes, and indexes will be intact:

DELETE FROM table_name;

The following SQL statement deletes all rows in the "Customers" table, without deleting the table:

Example

DELETE FROM Customers;

MySQL LIMIT Clause

The LIMIT clause is used to specify the number of records to return.

The LIMIT clause is useful on large tables with thousands of records. Returning a large number of records can impact performance.

LIMIT Syntax

SELECT column_name(s)
FROM table_name
WHERE condition
LIMIT number;

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany

MySQL LIMIT Examples

The following SQL statement selects the first three records from the "Customers" table:

Example

SELECT * FROM Customers
LIMIT 3;

ADD a WHERE CLAUSE

The following SQL statement selects the first three records from the "Customers" table, where the country is "Germany":

Example

SELECT * FROM Customers
WHERE Country='Germany'
LIMIT 3;

MySQL MIN() and MAX() Functions

The MIN() function returns the smallest value of the selected column.

The MAX() function returns the largest value of the selected column.

MIN() Syntax

SELECT MIN(column_name)
FROM table_name
WHERE condition;

MAX() Syntax

SELECT MAX(column_name)
FROM table_name
WHERE condition;

Demo Database

Below is a selection from the "Products" table in the Northwind sample database:

MIN() Example

The following SQL statement finds the price of the cheapest product:

Example

SELECT MIN(Price) AS SmallestPrice
FROM Products;

MAX() Example

The following SQL statement finds the price of the most expensive product:

Example

SELECT MAX(Price) AS LargestPrice
FROM Products;

MySQL COUNT(), AVG() and SUM() Functions

The COUNT() function returns the number of rows that match a specified criterion.

COUNT() Syntax

SELECT COUNT(column_name)
FROM table_name
WHERE condition;

The AVG() function returns the average value of a numeric column.

AVG() Syntax

SELECT AVG(column_name)
FROM table_name
WHERE condition;

The SUM() function returns the total sum of a numeric column.

SUM() Syntax

SELECT SUM(column_name)
FROM table_name
WHERE condition;

Demo Database

Below is a selection from the "Products" table in the Northwind sample database:

COUNT() Example

The following SQL statement finds the number of products:

Example

SELECT COUNT(ProductID)
FROM Products;

Note: NULL values are not counted.

AVG() Example

The following SQL statement finds the average price of all products:

Example

SELECT AVG(Price)
FROM Products;

Note: NULL values are ignored.

Demo Database

Below is a selection from the "OrderDetails" table in the Northwind sample database:

SUM() Example

The following SQL statement finds the sum of the "Quantity" fields in the "OrderDetails" table:

Example

SELECT SUM(Quantity)
FROM OrderDetails;

Note: NULL values are ignored.

MySQL LIKE Operator

The LIKE operator is used in a WHERE clause to search for a specified pattern in a column.

There are two wildcards often used in conjunction with the LIKE operator:

The percent sign and the underscore can also be used in combinations!

LIKE Syntax

SELECT column1, column2, ...
FROM table_name
WHERE columnN LIKE pattern;

Tip: You can also combine any number of conditions using AND or OR operators.

Here are some examples showing different LIKE operators with '%' and '_' wildcards:

LIKE Operator Description
WHERE CustomerName LIKE 'a%' Finds any values that start with "a"
WHERE CustomerName LIKE '%a' Finds any values that end with "a"
WHERE CustomerName LIKE '%or%' Finds any values that have "or" in any position
WHERE CustomerName LIKE '_r%' Finds any values that have "r" in the second position
WHERE CustomerName LIKE 'a_%' Finds any values that start with "a" and are at least 2 characters in length
WHERE CustomerName LIKE 'a__%' Finds any values that start with "a" and are at least 3 characters in length
WHERE ContactName LIKE 'a%o' Finds any values that start with "a" and end with "o"

Demo Database

The table below shows the complete "Customers" table from the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico

Example

SELECT * FROM Customers
WHERE CustomerName LIKE 'a%';

The following SQL statement selects all customers with a CustomerName ending with "a":

Example

SELECT * FROM Customers
WHERE CustomerName LIKE '%a';

The following SQL statement selects all customers with a CustomerName that have "or" in any position:

Example

SELECT * FROM Customers
WHERE CustomerName LIKE '%or%';

The following SQL statement selects all customers with a CustomerName that have "r" in the second position:

Example

SELECT * FROM Customers
WHERE CustomerName LIKE '_r%';

The following SQL statement selects all customers with a CustomerName that starts with "a" and are at least 3 characters in length:

Example

SELECT * FROM Customers
WHERE CustomerName LIKE 'a__%';

The following SQL statement selects all customers with a ContactName that starts with "a" and ends with "o":

Example

SELECT * FROM Customers
WHERE ContactName LIKE 'a%o';

The following SQL statement selects all customers with a CustomerName that does NOT start with "a":

Example

SELECT * FROM Customers
WHERE CustomerName NOT LIKE 'a%';

MySQL Wildcard Characters

A wildcard character is used to substitute one or more characters in a string.

Wildcard characters are used with the LIKE operator. The LIKE operator is used in a WHERE clause to search for a specified pattern in a column.

Wildcard Characters in MySQL

Symbol Description Example
% Represents zero or more characters bl% finds bl, black, blue, and blob
_ Represents a single character h_t finds hot, hat, and hit

The wildcards can also be used in combinations!

Here are some examples showing different LIKE operators with '%' and '_' wildcards:

LIKE Operator Description
WHERE CustomerName LIKE 'a%' Finds any values that start with "a"
WHERE CustomerName LIKE '%a' Finds any values that end with "a"
WHERE CustomerName LIKE '%or%' Finds any values that have "or" in any position
WHERE CustomerName LIKE '_r%' Finds any values that have "r" in the second position
WHERE CustomerName LIKE 'a_%_%' Finds any values that start with "a" and are at least 3 characters in length
WHERE ContactName LIKE 'a%o' Finds any values that start with "a" and end with "o"

Demo Database

The table below shows the complete "Customers" table from the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK
5 Berglunds snabbköp Christina Berglund Berguvsvägen 8 Luleå S-958 22 Sweden

Using the % Wildcard

The following SQL statement selects all customers with a City starting with "ber":

Example

SELECT * FROM Customers
WHERE City LIKE 'ber%';

The following SQL statement selects all customers with a City containing the pattern "es":

Example

SELECT * FROM Customers
WHERE City LIKE '%es%';

Using the _ Wildcard

The following SQL statement selects all customers with a City starting with any character, followed by "ondon":

Example

SELECT * FROM Customers
WHERE City LIKE '_ondon';

The following SQL statement selects all customers with a City starting with "L", followed by any character, followed by "n", followed by any character, followed by "on":

Example

SELECT * FROM Customers
WHERE City LIKE 'L_n_on';

The MySQL IN Operator

The IN operator allows you to specify multiple values in a WHERE clause.

The IN operator is a shorthand for multiple OR conditions.

IN Syntax

SELECT column_name(s)
FROM table_name
WHERE column_name IN (value1, value2, ...);

or:

SELECT column_name(s)
FROM table_name
WHERE column_name IN (SELECT STATEMENT);

Demo Database

The table below shows the complete "Customers" table from the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico

IN Operator Examples

The following SQL statement selects all customers that are located in "Germany", "France", or "UK":

SELECT * FROM Customers
WHERE Country IN ('Germany', 'France', 'UK');

The following SQL statement selects all customers that are NOT located in "Germany", "France", or "UK":

SELECT * FROM Customers
WHERE Country NOT IN ('Germany', 'France', 'UK');

The following SQL statement selects all customers that are from the same countries as the suppliers:

SELECT * FROM Customers
WHERE Country IN (SELECT Country FROM Suppliers);

MySQL BETWEEN Operator

The BETWEEN operator selects values within a given range. The values can be numbers, text, or dates.

The BETWEEN operator is inclusive: begin and end values are included.

BETWEEN Syntax

SELECT column_name(s)
FROM table_name
WHERE column_name BETWEEN value1 AND value2;

Demo Database

Below is a selection from the "Products" table in the Northwind sample database:

ProductID ProductName SupplierID CategoryID Unit Price
1 Chais 1 1 10 boxes x 20 bags 18
2 Chang 1 1 24 - 12 oz bottles 19
3 Aniseed Syrup 1 2 12 - 550 ml bottles 10

BETWEEN Example

The following SQL statement selects all products with a price between 10 and 20:

SELECT * FROM Products
WHERE Price BETWEEN 10 AND 20;

NOT BETWEEN Example

To display the products outside the range of the previous example, use NOT BETWEEN:

SELECT * FROM Products
WHERE Price NOT BETWEEN 10 AND 20;

BETWEEN with IN Example

The following SQL statement selects all products with a price between 10 and 20. In addition, do not show products with a CategoryID of 1, 2, or 3:

SELECT * FROM Products
WHERE Price BETWEEN 10 AND 20
AND CategoryID NOT IN (1, 2, 3);

BETWEEN Text Values Example

The following SQL statement selects all products with a ProductName between "Carnarvon Tigers" and "Mozzarella di Giovanni":

SELECT * FROM Products
WHERE ProductName BETWEEN 'Carnarvon Tigers' AND 'Mozzarella di Giovanni'
ORDER BY ProductName;

The following SQL statement selects all products with a ProductName between "Carnarvon Tigers" and "Chef Anton's Cajun Seasoning":

SELECT * FROM Products
WHERE ProductName BETWEEN "Carnarvon Tigers" AND "Chef Anton's Cajun Seasoning"
ORDER BY ProductName;

NOT BETWEEN Text Values Example

The following SQL statement selects all products with a ProductName not between "Carnarvon Tigers" and "Mozzarella di Giovanni":

SELECT * FROM Products
WHERE ProductName NOT BETWEEN 'Carnarvon Tigers' AND 'Mozzarella di Giovanni'
ORDER BY ProductName;

Sample Table

Below is a selection from the "Orders" table in the Northwind sample database:

OrderID CustomerID EmployeeID OrderDate ShipperID
10248 90 5 7/4/1996 3
10249 81 6 7/5/1996 1
10250 34 4 7/8/1996 2

BETWEEN Dates Example

The following SQL statement selects all orders with an OrderDate between '01-July-1996' and '31-July-1996':

SELECT * FROM Orders
WHERE OrderDate BETWEEN '1996-07-01' AND '1996-07-31';

MySQL Aliases

Aliases are used to give a table, or a column in a table, a temporary name. Aliases are often used to make column names more readable. An alias only exists for the duration of that query. An alias is created with the AS keyword.

Alias Column Syntax

SELECT column_name AS alias_name
FROM table_name;

Alias Table Syntax

SELECT column_name(s)
FROM table_name AS alias_name;

Demo Database

In this tutorial we will use the well-known Northwind sample database. Below is a selection from the "Customers" table:

CustomerID CustomerName ContactName Address City PostalCode Country
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK

And a selection from the "Orders" table:

OrderID CustomerID EmployeeID OrderDate ShipperID
10354 58 8 1996-11-14 3
10355 4 6 1996-11-15 1
10356 86 6 1996-11-18 2

Alias for Columns Examples

The following SQL statement creates two aliases, one for the CustomerID column and one for the CustomerName column:

SELECT CustomerID AS ID, CustomerName AS Customer
FROM Customers;

The following SQL statement creates two aliases, one for the CustomerName column and one for the ContactName column. Note: Single or double quotation marks are required if the alias name contains spaces:

Example

SELECT CustomerName AS Customer, ContactName AS "Contact Person"
FROM Customers;

The following SQL statement creates an alias named "Address" that combine four columns (Address, PostalCode, City and Country):

Example

SELECT CustomerName, CONCAT_WS(', ', Address, PostalCode, City, Country) AS Address
FROM Customers;

Alias for Tables Example

The following SQL statement selects all the orders from the customer with CustomerID=4 (Around the Horn). We use the "Customers" and "Orders" tables, and give them the table aliases of "c" and "o" respectively (Here we use aliases to make the SQL shorter):

Example

SELECT o.OrderID, o.OrderDate, c.CustomerName
FROM Customers AS c, Orders AS o
WHERE c.CustomerName='Around the Horn' AND c.CustomerID=o.CustomerID;

The following SQL statement is the same as above, but without aliases:

Example

SELECT Orders.OrderID, Orders.OrderDate, Customers.CustomerName
FROM Customers, Orders
WHERE Customers.CustomerName='Around the Horn' AND Customers.CustomerID=Orders.CustomerID;

MySQL Joining Tables

A JOIN clause is used to combine rows from two or more tables, based on a related column between them.

Let's look at a selection from the "Orders" table:

OrderID CustomerID OrderDate
10308 2 1996-09-18
10309 37 1996-09-19
10310 77 1996-09-20

Then, look at a selection from the "Customers" table:

CustomerID CustomerName ContactName Country
1 Alfreds Futterkiste Maria Anders Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Mexico
3 Antonio Moreno Taquería Antonio Moreno Mexico

Notice that the "CustomerID" column in the "Orders" table refers to the "CustomerID" in the "Customers" table. The relationship between the two tables above is the "CustomerID" column.

Then, we can create the following SQL statement (that contains an INNER JOIN), that selects records that have matching values in both tables:

Example

SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate
FROM Orders
INNER JOIN Customers ON Orders.CustomerID=Customers.CustomerID;

and it will produce something like this:

OrderID CustomerName OrderDate
10308 Ana Trujillo Emparedados y helados 9/18/1996
10365 Antonio Moreno Taquería 11/27/1996
10383 Around the Horn 12/16/1996
10355 Around the Horn 11/15/1996
10278 Berglunds snabbköp 8/12/1996

Supported Types of Joins in MySQL

MySQL INNER JOIN

MySQL INNER JOIN

MySQL LEFT JOIN

MySQL LEFT JOIN

MySQL RIGHT JOIN

MySQL RIGHT JOIN

MySQL CROSS JOIN

MySQL CROSS JOIN

MySQL INNER JOIN Keyword

The INNER JOIN keyword selects records that have matching values in both tables.

MySQL INNER JOIN

INNER JOIN Syntax

SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the "Orders" table:

OrderID CustomerID EmployeeID OrderDate ShipperID
10308 2 7 1996-09-18 3
10309 37 3 1996-09-19 1
10310 77 8 1996-09-20 2

And a selection from the "Customers" table:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico

MySQL INNER JOIN Example

The following SQL statement selects all orders with customer information:

Example

SELECT Orders.OrderID, Customers.CustomerName
FROM Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

Note: The INNER JOIN keyword selects all rows from both tables as long as there is a match between the columns. If there are records in the "Orders" table that do not have matches in "Customers", these orders will not be shown!

JOIN Three Tables

The following SQL statement selects all orders with customer and shipper information:

SELECT Orders.OrderID, Customers.CustomerName, Shippers.ShipperName
FROM ((Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID)
INNER JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID);

MySQL LEFT JOIN Keyword

The LEFT JOIN keyword returns all records from the left table (table1), and the matching records (if any) from the right table (table2).

MySQL LEFT JOIN

LEFT JOIN Syntax

SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the "Customers" table:

CustomerID CustomerName ContactName Address City PostalCode Country
1

 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico

And a selection from the "Orders" table:

OrderID CustomerID EmployeeID OrderDate ShipperID
10308 2 7 1996-09-18 3
10309 37 3 1996-09-19 1
10310 77 8 1996-09-20 2

MySQL LEFT JOIN Example

The following SQL statement will select all customers, and any orders they might have:

Example

SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
LEFT JOIN Orders ON Customers.CustomerID = Orders.CustomerID
ORDER BY Customers.CustomerName;

MySQL RIGHT JOIN Keyword

The RIGHT JOIN keyword returns all records from the right table (table2), and the matching records (if any) from the left table (table1).

MySQL RIGHT JOIN

RIGHT JOIN Syntax

SELECT column_name(s)
FROM table1
RIGHT JOIN table2
ON table1.column_name = table2.column_name;

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the "Orders" table:

OrderID CustomerID EmployeeID OrderDate ShipperID
10308 2 7 1996-09-18 3
10309 37 3 1996-09-19 1
10310 77 8 1996-09-20 2

And a selection from the "Employees" table:

EmployeeID LastName FirstName BirthDate Photo
1 Davolio Nancy 12/8/1968 EmpID1.pic
2 Fuller Andrew 2/19/1952 EmpID2.pic
3 Leverling Janet 8/30/1963 EmpID3.pic

MySQL RIGHT JOIN Example

The following SQL statement will return all employees, and any orders they might have placed:

Example

SELECT Orders.OrderID, Employees.LastName, Employees.FirstName
FROM Orders
RIGHT JOIN Employees ON Orders.EmployeeID = Employees.EmployeeID
ORDER BY Orders.OrderID;
Note: The RIGHT JOIN keyword returns all records from the right table (Employees), even if there are no matches in the left table (Orders).

SQL CROSS JOIN Keyword

The CROSS JOIN keyword returns all records from both tables (table1 and table2).

MySQL CROSS JOIN

CROSS JOIN Syntax

SELECT column_name(s)
FROM table1
CROSS JOIN table2;

Note: CROSS JOIN can potentially return very large result-sets!

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the "Customers" table:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico

And a selection from the "Orders" table:

OrderID CustomerID EmployeeID OrderDate ShipperID
10308 2 7 1996-09-18 3
10309 37 3 1996-09-19 1
10310 77 8 1996-09-20 2

MySQL CROSS JOIN Example

The following SQL statement selects all customers, and all orders:

Example

SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
CROSS JOIN Orders;
Try it Yourself »

Note: The CROSS JOIN keyword returns all matching records from both tables whether the other table matches or not. So, if there are rows in "Customers" that do not have matches in "Orders", or if there are rows in "Orders" that do not have matches in "Customers", those rows will be listed as well.

If you add a WHERE clause (if table1 and table2 has a relationship), the CROSS JOIN will produce the same result as the INNER JOIN clause:

Example

SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
CROSS JOIN Orders
WHERE Customers.CustomerID=Orders.CustomerID;

MySQL Self Join

A self join is a regular join, but the table is joined with itself.

Self Join Syntax

SELECT column_name(s)
FROM table1 T1, table1 T2
WHERE condition;

T1 and T2 are different table aliases for the same table.

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the "Customers" table:

CustomerID CustomerName ContactName Address City PostalCode Country
1

 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico

MySQL Self Join Example

The following SQL statement matches customers that are from the same city:

Example

SELECT A.CustomerName AS CustomerName1, B.CustomerName AS CustomerName2, A.City
FROM Customers A, Customers B
WHERE A.CustomerID <> B.CustomerID
AND A.City = B.City
ORDER BY A.City;

MySQL UNION Operator

The UNION operator is used to combine the result-set of two or more SELECT statements.

UNION Syntax

SELECT column_name(s) FROM table1
UNION
SELECT column_name(s) FROM table2;

UNION ALL Syntax

The UNION operator selects only distinct values by default. To allow duplicate values, use UNION ALL:

SELECT column_name(s) FROM table1
UNION ALL
SELECT column_name(s) FROM table2;

Note: The column names in the result-set are usually equal to the column names in the first SELECT statement.

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the "Customers" table:

CustomerID CustomerName ContactName Address City PostalCode Country
1

 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico

And a selection from the "Suppliers" table:

SupplierID SupplierName ContactName Address City PostalCode Country
1 Exotic Liquid Charlotte Cooper 49 Gilbert St. London EC1 4SD UK
2 New Orleans Cajun Delights Shelley Burke P.O. Box 78934 New Orleans 70117 USA
3 Grandma Kelly's Homestead Regina Murphy 707 Oxford Rd. Ann Arbor 48104 USA

SQL UNION ALL Example

The following SQL statement returns the cities (only distinct values) from both the "Customers" and the "Suppliers" table:

Example

SELECT City FROM Customers
UNION
SELECT City FROM Suppliers
ORDER BY City;

Note: If some customers or suppliers have the same city, each city will only be listed once, because UNION selects only distinct values. Use UNION ALL to also select duplicate values!

SQL UNION ALL Example

The following SQL statement returns the cities (duplicate values also) from both the "Customers" and the "Suppliers" table:

Example

SELECT City FROM Customers
UNION ALL
SELECT City FROM Suppliers
ORDER BY City;

SQL UNION With WHERE

The following SQL statement returns the German cities (only distinct values) from both the "Customers" and the "Suppliers" table:

Example

SELECT City, Country FROM Customers
WHERE Country='Germany'
UNION
SELECT City, Country FROM Suppliers
WHERE Country='Germany'
ORDER BY City;

SQL UNION ALL With WHERE

The following SQL statement returns the German cities (duplicate values also) from both the "Customers" and the "Suppliers" table:

Example

SELECT City, Country FROM Customers
WHERE Country='Germany'
UNION ALL
SELECT City, Country FROM Suppliers
WHERE Country='Germany'
ORDER BY City;

Another UNION Example

The following SQL statement lists all customers and suppliers:

Example

SELECT 'Customer' AS Type, ContactName, City, Country
FROM Customers
UNION
SELECT 'Supplier', ContactName, City, Country
FROM Suppliers;

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK
5 Berglunds snabbköp Christina Berglund Berguvsvägen 8 Luleå S-958 22 Sweden

MySQL GROUP BY Examples

The following SQL statement lists the number of customers in each country:

Example

SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country;
Try it Yourself »

The following SQL statement lists the number of customers in each country, sorted high to low:

Example

SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country
ORDER BY COUNT(CustomerID) DESC;
Try it Yourself »

Demo Database

Below is a selection from the "Orders" table in the Northwind sample database:

OrderID CustomerID EmployeeID OrderDate ShipperID
10248 90 5 1996-07-04 3
10249 81 6 1996-07-05 1
10250 34 4 1996-07-08 2

And a selection from the "Shippers" table:

ShipperID ShipperName
1 Speedy Express
2 United Package
3 Federal Shipping

GROUP BY With JOIN Example

The following SQL statement lists the number of orders sent by each shipper:

Example

SELECT Shippers.ShipperName, COUNT(Orders.OrderID) AS NumberOfOrders FROM Orders
LEFT JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID
GROUP BY ShipperName;

MySQL HAVING Clause

The HAVING clause was added to SQL because the WHERE keyword cannot be used with aggregate functions.

HAVING Syntax

SELECT column_name(s)
FROM table_name
WHERE condition
GROUP BY column_name(s)
HAVING condition
ORDER BY column_name(s);

Demo Database

Below is a selection from the "Customers" table in the Northwind sample database:

CustomerID CustomerName ContactName Address City PostalCode Country
1

 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4

 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK
5 Berglunds snabbköp Christina Berglund Berguvsvägen 8 Luleå S-958 22 Sweden

MySQL HAVING Examples

The following SQL statement lists the number of customers in each country. Only include countries with more than 5 customers:

Example

SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country
HAVING COUNT(CustomerID) > 5;
Try it Yourself »

The following SQL statement lists the number of customers in each country, sorted high to low (Only include countries with more than 5 customers):

Example

SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country
HAVING COUNT(CustomerID) > 5
ORDER BY COUNT(CustomerID) DESC;
Try it Yourself »

Demo Database

Below is a selection from the "Orders" table in the Northwind sample database:

OrderID CustomerID EmployeeID OrderDate ShipperID
10248 90 5 1996-07-04 3
10249 81 6 1996-07-05 1
10250 34 4 1996-07-08 2

And a selection from the "Employees" table:

EmployeeID LastName FirstName BirthDate Photo Notes
1 Davolio Nancy 1968-12-08 EmpID1.pic Education includes a BA....
2 Fuller Andrew 1952-02-19 EmpID2.pic Andrew received his BTS....
3 Leverling Janet 1963-08-30 EmpID3.pic Janet has a BS degree....

More HAVING Examples

The following SQL statement lists the employees that have registered more than 10 orders:

Example

SELECT Employees.LastName, COUNT(Orders.OrderID) AS NumberOfOrders
FROM (Orders
INNER JOIN Employees ON Orders.EmployeeID = Employees.EmployeeID)
GROUP BY LastName
HAVING COUNT(Orders.OrderID) > 10;
Try it Yourself »

The following SQL statement lists if the employees "Davolio" or "Fuller" have registered more than 25 orders:

Example

SELECT Employees.LastName, COUNT(Orders.OrderID) AS NumberOfOrders
FROM Orders
INNER JOIN Employees ON Orders.EmployeeID = Employees.EmployeeID
WHERE LastName = 'Davolio' OR LastName = 'Fuller'
GROUP BY LastName
HAVING COUNT(Orders.OrderID) > 25;

MySQL EXISTS Operator

The EXISTS operator is used to test for the existence of any record in a subquery.

The EXISTS operator returns TRUE if the subquery returns one or more records.

EXISTS Syntax

SELECT column_name(s)
FROM table_name
WHERE EXISTS
(SELECT column_name FROM table_name WHERE condition);

Demo Database

Below is a selection from the "Products" table in the Northwind sample database:

ProductID ProductName SupplierID CategoryID Unit Price
1 Chais 1 1 10 boxes x 20 bags 18
2 Chang 1 1 24 - 12 oz bottles 19
3 Aniseed Syrup 1 2 12 - 550 ml bottles 10
4 Chef Anton's Cajun Seasoning 2 2 48 - 6 oz jars 22
5 Chef Anton's Gumbo Mix 2 2 36 boxes 21.35

And a selection from the "Suppliers" table:

SupplierID SupplierName ContactName Address City PostalCode Country
1 Exotic Liquid Charlotte Cooper 49 Gilbert St. London EC1 4SD UK
2 New Orleans Cajun Delights Shelley Burke P.O. Box 78934 New Orleans 70117 USA
3 Grandma Kelly's Homestead Regina Murphy 707 Oxford Rd. Ann Arbor 48104 USA
4 Tokyo Traders Yoshi Nagase 9-8 Sekimai Musashino-shi Tokyo 100 Japan

MySQL EXISTS Examples

The following SQL statement returns TRUE and lists the suppliers with a product price less than 20:

Example

SELECT SupplierName
FROM Suppliers
WHERE EXISTS (SELECT ProductName FROM Products WHERE Products.SupplierID = Suppliers.supplierID AND Price < 20);
Try it Yourself »

The following SQL statement returns TRUE and lists the suppliers with a product price equal to 22:

Example

SELECT SupplierName
FROM Suppliers
WHERE EXISTS (SELECT ProductName FROM Products WHERE Products.SupplierID = Suppliers.supplierID AND Price = 22);

The MySQL ANY and ALL Operators

The ANY and ALL operators allow you to perform a comparison between a single column value and a range of other values.

The ANY Operator

The ANY operator:

ANY means that the condition will be true if the operation is true for any of the values in the range.

ANY Syntax

SELECT column_name(s)
FROM table_name
WHERE column_name operator ANY
(SELECT column_name
FROM table_name
WHERE condition);

Note: The operator must be a standard comparison operator (=, <>, !=, >, >=, <, or <=).

The ALL Operator

The ALL operator:

ALL means that the condition will be true only if the operation is true for all values in the range.

ALL Syntax With SELECT

SELECT ALL column_name(s)
FROM table_name
WHERE condition;

ALL Syntax With WHERE or HAVING

SELECT column_name(s)
FROM table_name
WHERE column_name operator ALL
(SELECT column_name
FROM table_name
WHERE condition);

Note: The operator must be a standard comparison operator (=, <>, !=, >, >=, <, or <=).

Demo Database

Below is a selection from the "Products" table in the Northwind sample database:

ProductID ProductName SupplierID CategoryID Unit Price
1 Chais 1 1 10 boxes x 20 bags 18
2 Chang 1 1 24 - 12 oz bottles 19
3 Aniseed Syrup 1 2 12 - 550 ml bottles 10
4 Chef Anton's Cajun Seasoning 2 2 48 - 6 oz jars 22
5 Chef Anton's Gumbo Mix 2 2 36 boxes 21.35
6 Grandma's Boysenberry Spread 3 2 12 - 8 oz jars 25
7 Uncle Bob's Organic Dried Pears 3 7 12 - 1 lb pkgs. 30
8 Northwoods Cranberry Sauce 3 2 12 - 12 oz jars 40
9 Mishi Kobe Niku 4 6 18 - 500 g pkgs. 97

And a selection from the "OrderDetails" table:

OrderDetailID OrderID ProductID Quantity
1 10248 11 12
2 10248 42 10
3 10248 72 5
4 10249 14 9
5 10249 51 40
6 10250 41 10
7 10250 51 35
8 10250 65 15
9 10251 22 6
10 10251 57 15

SQL ANY Examples

The following SQL statement lists the ProductName if it finds ANY records in the OrderDetails table has Quantity equal to 10 (this will return TRUE because the Quantity column has some values of 10):

Example

SELECT ProductName
FROM Products
WHERE ProductID = ANY
(SELECT ProductID
FROM OrderDetails
WHERE Quantity = 10);
Try it Yourself »

The following SQL statement lists the ProductName if it finds ANY records in the OrderDetails table has Quantity larger than 99 (this will return TRUE because the Quantity column has some values larger than 99):

Example

SELECT ProductName
FROM Products
WHERE ProductID = ANY
(SELECT ProductID
FROM OrderDetails
WHERE Quantity > 99);
Try it Yourself »

The following SQL statement lists the ProductName if it finds ANY records in the OrderDetails table has Quantity larger than 1000 (this will return FALSE because the Quantity column has no values larger than 1000):

Example

SELECT ProductName
FROM Products
WHERE ProductID = ANY
(SELECT ProductID
FROM OrderDetails
WHERE Quantity > 1000);
Try it Yourself »

SQL ALL Examples

The following SQL statement lists ALL the product names:

Example

SELECT ALL ProductName
FROM Products
WHERE TRUE;
Try it Yourself »

The following SQL statement lists the ProductName if ALL the records in the OrderDetails table has Quantity equal to 10. This will of course return FALSE because the Quantity column has many different values (not only the value of 10):

Example

SELECT ProductName
FROM Products
WHERE ProductID = ALL
(SELECT ProductID
FROM OrderDetails
WHERE Quantity = 10);

MySQL INSERT INTO SELECT Statement

The INSERT INTO SELECT statement copies data from one table and inserts it into another table.

The INSERT INTO SELECT statement requires that the data types in source and target tables matches.

Note: The existing records in the target table are unaffected.

INSERT INTO SELECT Syntax

Copy all columns from one table to another table:

INSERT INTO table2
SELECT * FROM table1
WHERE condition;

Copy only some columns from one table into another table:

INSERT INTO table2 (column1, column2, column3, ...)
SELECT column1, column2, column3, ...
FROM table1
WHERE condition;

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the "Customers" table:

CustomerID CustomerName ContactName Address City PostalCode Country
1

 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico

And a selection from the "Suppliers" table:

SupplierID SupplierName ContactName Address City Postal Code Country
1 Exotic Liquid Charlotte Cooper 49 Gilbert St. Londona EC1 4SD UK
2 New Orleans Cajun Delights Shelley Burke P.O. Box 78934 New Orleans 70117 USA
3 Grandma Kelly's Homestead Regina Murphy 707 Oxford Rd. Ann Arbor 48104 USA

MySQL INSERT INTO SELECT Examples

The following SQL statement copies "Suppliers" into "Customers" (the columns that are not filled with data will contain NULL):

Example

INSERT INTO Customers (CustomerName, City, Country)
SELECT SupplierName, City, Country FROM Suppliers;

The following SQL statement copies "Suppliers" into "Customers" (fill all columns):

Example

INSERT INTO Customers (CustomerName, ContactName, Address, City, PostalCode, Country)
SELECT SupplierName, ContactName, Address, City, PostalCode, Country FROM Suppliers;

The following SQL statement copies only the German suppliers into "Customers":

Example

INSERT INTO Customers (CustomerName, City, Country)
SELECT SupplierName, City, Country FROM Suppliers WHERE Country='Germany';

MySQL CASE Statement

The CASE statement goes through conditions and returns a value when the first condition is met (like an if-then-else statement). So, once a condition is true, it will stop reading and return the result. If no conditions are true, it returns the value in the ELSE clause.

If there is no ELSE part and no conditions are true, it returns NULL.

CASE Syntax

CASE
WHEN condition1 THEN result1
WHEN condition2 THEN result2
WHEN conditionN THEN resultN
ELSE result
END;

Demo Database

Below is a selection from the "OrderDetails" table in the Northwind sample database:

OrderDetailID OrderID ProductID Quantity
1 10248 11 12
2 10248 42 10
3 10248 72 5
4 10249 14 9
5 10249 51 40

MySQL CASE Examples

The following SQL goes through conditions and returns a value when the first condition is met:

Example

SELECT OrderID, Quantity,
CASE
WHEN Quantity > 30 THEN 'The quantity is greater than 30'
WHEN Quantity = 30 THEN 'The quantity is 30'
ELSE 'The quantity is under 30'
END AS QuantityText
FROM OrderDetails;
Try it Yourself »

The following SQL will order the customers by City. However, if City is NULL, then order by Country:

Example

SELECT CustomerName, City, Country
FROM Customers
ORDER BY
(CASE
WHEN City IS NULL THEN Country
ELSE City
END);

MySQL IFNULL() and COALESCE() Functions

Look at the following "Products" table:

P_Id ProductName UnitPrice UnitsInStock UnitsOnOrder
1 Jarlsberg 10.45 16 15
2 Mascarpone 32.56 23
3 Gorgonzola 15.67 9 20

Suppose that the "UnitsOnOrder" column is optional, and may contain NULL values.

Look at the following SELECT statement:

SELECT ProductName, UnitPrice * (UnitsInStock + UnitsOnOrder)
FROM Products;

In the example above, if any of the "UnitsOnOrder" values are NULL, the result will be NULL.

MySQL IFNULL() Function

The MySQL IFNULL() function lets you return an alternative value if an expression is NULL.

The example below returns 0 if the value is NULL:

SELECT ProductName, UnitPrice * (UnitsInStock + IFNULL(UnitsOnOrder, 0))
FROM Products;

MySQL COALESCE() Function

Or we can use the COALESCE() function, like this:

SELECT ProductName, UnitPrice * (UnitsInStock + COALESCE(UnitsOnOrder, 0))
FROM Products;

MySQL Comments

Comments are used to explain sections of SQL statements, or to prevent execution of SQL statements.

Single Line Comments

Single line comments start with --.

Any text between -- and the end of the line will be ignored (will not be executed).

The following example uses a single-line comment as an explanation:

Example

-- Select all:
SELECT * FROM Customers;
Try it Yourself »

The following example uses a single-line comment to ignore the end of a line:

Example

SELECT * FROM Customers -- WHERE City='Berlin';
Try it Yourself »

The following example uses a single-line comment to ignore a statement:

Example

-- SELECT * FROM Customers;
SELECT * FROM Products;
Try it Yourself »

Multi-line Comments

Multi-line comments start with /* and end with */.

Any text between /* and */ will be ignored.

The following example uses a multi-line comment as an explanation:

Example

/*Select all the columns
of all the records
in the Customers table:*/
SELECT * FROM Customers;
Try it Yourself »

The following example uses a multi-line comment to ignore many statements:

Example

/*SELECT * FROM Customers;
SELECT * FROM Products;
SELECT * FROM Orders;
SELECT * FROM Categories;*/
SELECT * FROM Suppliers;
Try it Yourself »

To ignore just a part of a statement, also use the /* */ comment.

The following example uses a comment to ignore part of a line:

Example

SELECT CustomerName, /*City,*/ Country FROM Customers;
Try it Yourself »

The following example uses a comment to ignore part of a statement:

Example

SELECT * FROM Customers WHERE (CustomerName LIKE 'L%'
OR CustomerName LIKE 'R%' /*OR CustomerName LIKE 'S%'
OR CustomerName LIKE 'T%'*/ OR CustomerName LIKE 'W%')
AND Country='USA'
ORDER BY CustomerName;

MySQL Arithmetic Operators

Operator Description Example
+ Add Try it
- Subtract Try it
* Multiply Try it
/ Divide Try it
% Modulo Try it

MySQL Bitwise Operators

Operator Description
& Bitwise AND
| Bitwise OR
^ Bitwise exclusive OR

MySQL Comparison Operators

Operator Description Example
= Equal to Try it
> Greater than Try it
< Less than Try it
>= Greater than or equal to Try it
<= Less than or equal to Try it
<> Not equal to Try it

MySQL Compound Operators

Operator Description
+= Add equals
-= Subtract equals
*= Multiply equals
/= Divide equals
%= Modulo equals
&= Bitwise AND equals
^-= Bitwise exclusive equals
|*= Bitwise OR equals

MySQL Logical Operators

Operator Description Example
ALL TRUE if all of the subquery values meet the condition Try it
AND TRUE if all the conditions separated by AND is TRUE Try it
ANY TRUE if any of the subquery values meet the condition Try it
BETWEEN TRUE if the operand is within the range of comparisons Try it
EXISTS TRUE if the subquery returns one or more records Try it
IN TRUE if the operand is equal to one of a list of expressions Try it
LIKE TRUE if the operand matches a pattern Try it
NOT Displays a record if the condition(s) is NOT TRUE Try it
OR TRUE if any of the conditions separated by OR is TRUE Try it
SOME TRUE if any of the subquery values meet the condition Try it