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MySQL AUTO_INCREMENT - GeeksforGeeks

Last Updated : 23 Jul, 2025

In MySQL, the AUTO_INCREMENT attribute is used to generate a unique identifier for new rows in a table. This attribute is often applied to primary key columns to ensure that each row can be uniquely identified. This article will explore the AUTO_INCREMENT attribute, how to use it, and various considerations to keep in mind.

An attribute that can be added to a column is AUTO_INCREMENT which generates an identification number for every record that is added to a table. Usually associated with the PRIMARY KEY constraint, it helps to achieve that each record possesses a unique value, which is rather important for searching data.

Syntax:

The 'AUTO_INCREMENT' attribute is added to a column definition in a CREATE TABLE or ALTER TABLE statement. Here is the basic syntax:

CREATE TABLE table_name (

column1 datatype AUTO_INCREMENT,

column2 datatype,

...

PRIMARY KEY (column1)

);

For an existing table, you can add AUTO_INCREMENT using:

ALTER TABLE table_name MODIFY column_name datatype AUTO_INCREMENT;

Let's create a table named 'employees' with an AUTO_INCREMENT column.

CREATE TABLE employees (    
id INT AUTO_INCREMENT,   
name VARCHAR(50),    
position VARCHAR(50),    
PRIMARY KEY (id)
);

Now, let's insert some data into the 'employees' table and observe how the AUTO_INCREMENT column behaves.

INSERT INTO employees (name, position) VALUES ('Alice', 'Manager');
INSERT INTO employees (name, position) VALUES ('Bob', 'Developer');
INSERT INTO employees (name, position) VALUES ('Charlie', 'Designer');

To verify the inserted data and see the AUTO_INCREMENT values, execute:

SELECT * FROM employees;

This query will retrieve all records from the employees table. The expected output will look like this:

You can set a specific starting value for the 'AUTO_INCREMENT' column using the 'ALTER TABLE' statement:

ALTER TABLE employee AUTO_INCREMENT = 1000;

Now, let's insert a new row into the employees table to see the effect of setting the AUTO_INCREMENT value to 1000:

INSERT INTO employees (name, position) VALUES ('Dave', 'Tester');

SELECT * FROM employees;

Output:

By setting the AUTO_INCREMENT value to 1000, the next inserted row after setting this value receives an id of 1000, as shown in the table.

When you delete rows from a table, the 'AUTO_INCREMENT' value does not automatically reset. For example, if you delete the last row, the next insert will continue with the next incremented value. Here is an example to illustrate this:

• Suppose the table initially has the following rows: id name position 1 Alice Manager 2 Bob Developer 3 Charlie Designer
• If you delete the last row:

DELETE FROM employees WHERE id = 3;

• The table will now look like this: id name position 1 Alice Manager 2 Bob Developer
• Inserting a new row will result in the following:

INSERT INTO employees (name, position) VALUES ('Dave', 'Tester');

Output:

1. Primary Key Requirement: The AUTO_INCREMENT column must be defined as a key (typically the primary key) for the table.
   
2. Only One AUTO_INCREMENT Column: Each table can have only one AUTO_INCREMENT column.
   
3. Integer Data Type: The AUTO_INCREMENT attribute can be used only with integer types.
   
4. Handling Duplicates: Ensure that the AUTO_INCREMENT column is unique and not manually set to a value that might cause duplicates

The AUTO_INCREMENT attribute in MySQL is an important feature for the generation of the new table record’s automatically running number ID’s. It makes it easy to ensure that each record within a given table has a primary key, which is very crucial for dictating the integrity and accessibility of the records within the database. With AUTO_INCREMENT being used properly, you will have the sense of improving your ability in database management.

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