MySQL: Sequences (AUTO_INCREMENT) - TechOnTheNet

Example

Let's look at an example of how to use a sequence or the AUTO_INCREMENT attribute in MySQL.

For example:

CREATE TABLE contacts ( contact_id INT(11) NOT NULL AUTO_INCREMENT, last_name VARCHAR(30) NOT NULL, first_name VARCHAR(25), birthday DATE, CONSTRAINT contacts_pk PRIMARY KEY (contact_id) );

This MySQL AUTO_INCREMENT example creates a table called contacts which has 4 columns and one primary key:

• The first column is called contact_id which is created as an INT datatype (maximum 11 digits in length) and can not contain NULL values. It is set as an AUTO_INCREMENT field which means that it is an autonumber field (starting at 1, and incrementing by 1, unless otherwise specified.)
• The second column is called last_name which is a VARCHAR datatype (maximum 30 characters in length) and can not contain NULL values.
• The third column is called first_name which is a VARCHAR datatype (maximum 25 characters in length) and can contain NULL values.
• The fourth column is called birthday which is a DATE datatype and can contain NULL values.
• The primary key is called contacts_pk and is set to the contact_id column.

Set AUTO_INCREMENT starting value

Now that you've created a table using the AUTO_INCREMENT attribute, how can you change the starting value for the AUTO_INCREMENT field if you don't want to start at 1?

You can use the ALTER TABLE statement to change or set the next value assigned by the AUTO_INCREMENT.

Syntax

In MySQL, the syntax to change the starting value for an AUTO_INCREMENT column using the ALTER TABLE statement is:

ALTER TABLE table_name AUTO_INCREMENT = start_value; table_name The name of the table whose AUTO_INCREMENT value you wish to change. Since a table in MySQL can only contain one AUTO_INCREMENT column, you are only required to specify the table name that contains the sequence. You do not need to specify the name of the column that contains the AUTO_INCREMENT value. start_value The next value in the sequence to assign in the AUTO_INCREMENT column.

Example

Let's look at an example of how to change the starting value for the AUTO_INCREMENT column in a table in MySQL.

For example:

ALTER TABLE contacts AUTO_INCREMENT = 50;

This MySQL AUTO_INCREMENT example would change the next value in the AUTO_INCREMENT field (ie: next value in the sequence) to 50 for the contact_id field in the contacts table.

Other Related Tutorials

Here are some other tutorials to help you learn more about sequences in MySQL:

Reset the Next Value in Sequence