MySQL AUTO_INCREMENT

In MySQL, the AUTO_INCREMENT attribute automatically generates a unique numeric value for each new row in a table. It is commonly used with primary key columns to ensure every record can be uniquely identified.

AUTO_INCREMENT assigns a sequential ID to each new record automatically.
It is typically used with the PRIMARY KEY to maintain uniqueness.
Helps in efficient data retrieval and ensures no duplicate identifiers exist.

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;

Working with MySQL 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)
);

Inserting Data into the Table

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');

Viewing the Table Data

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

SELECT * FROM employees;

Output:

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

Modifying AUTO_INCREMENT Values

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

ALTER TABLE employee AUTO_INCREMENT = 1000;

Inserting Additional Data

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');

Viewing the Table Data Again

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.

Deleting Rows and AUTO_INCREMENT

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:

If you delete the last row:

DELETE FROM employees WHERE id = 3;

The table will now look like this:

Inserting a new row will result in the following:

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