MySQL Reset Auto Increment Values

 MySQL Reset Auto Increment Values

Summary: in this tutorial, we  will show you various ways to reset the auto-increment values of AUTO_INCREMENT columns in MySQL.

MySQL provides you with a useful feature called auto-increment. You can assign the AUTO_INCREMENT attribute to a column of a table to generate a unique identity for the new row. Typically, you use the AUTO_INCREMENT attribute for the primary key column of the table.

Whenever you insert a new row into a table, MySQL automatically assigns a sequence number to the AUTO_INCREMENT column.

For example, if the table has eight rows and you insert a new row without specifying the value for the auto-increment column, MySQL will automatically insert a new row with id value 9.

Sometimes, you may need to reset the value of the auto-increment column so that the first record’s identity that you insert into the table starts from a specific number e.g., 1.

In MySQL, you can reset auto-increment values in various ways.

MySQL reset auto-increment value examples

First, create a table named  tmp and assign the AUTO_INCREMENT attribute to the id  primary key column.

CREATE TABLE tmp (
  id INT NOT NULL AUTO_INCREMENT,
  name VARCHAR(45) DEFAULT NULL,
  PRIMARY KEY (id)
);

Second, insert some sample data into the tmp  table:

INSERT INTO tmp(name)
VALUES('test 1'),
      ('test 2'),
      ('test 3');

Third, query the tmp  table to verify the insert operation:

SELECT 
    *
FROM
    tmp;

We have three rows with values of ID column are 1, 2, and 3. Perfect! It is time to practice resetting the auto-increment value of the ID column.

Using the ALTER TABLE statement

You can reset the auto-increment value by using the ALTER TABLE statement. The syntax of the ALTER TABLE  statement to reset the auto-increment value is as follows:

ALTER TABLE table_name AUTO_INCREMENT = value;

You specify the table name after the ALTER TABLE clause and the value which you want to reset to in the expression AUTO_INCREMENT=value.

Notice that the value must be greater than or equal to the current maximum value of the auto-increment column.

Let’s delete the last record in the tmp  table with id value 3:

DELETE FROM tmp 
WHERE
    ID = 3;

If you insert a new row, MySQL will assign 4 to the id column of the new row. However, you can reset the number generated by MySQL to 3 by using a ALTER TABLE  a statement like the following:

ALTER TABLE tmp AUTO_INCREMENT = 3;

Now, let’s try to insert a new row into the tmp  table  and query data from it to see the effect:

INSERT INTO tmp(name)
VALUES ('MySQL example 3');

SELECT 
    *
FROM
    tmp;

We have three rows with the last auto-increment value is 3 instead of 4, which is what we expected.

Using the TRUNCATE TABLE statement

The TRUNCATE TABLE statement removes all the data from a table and resets the auto-increment value to zero.

The following illustrates the syntax of the TRUNCATE TABLE  statement:

TRUNCATE TABLE table_name;

By using the TRUNCATE TABLE  the statement, you delete all data from the table permanently and reset the auto-increment value to zero.

Using DROP  TABLE and CREATE TABLE statements

You can use a pair of statements: DROP TABLE and CREATE TABLE to reset the auto-increment column. Note that this method deletes all data from the table permanently.

Like the TRUNCATE TABLE  the statement, those statements drop the table and recreate it, therefore, the value of the auto-increment is reset to zero.

DROP TABLE table_name;
CREATE TABLE table_name(...);

In this tutorial, you have learned how to reset the auto-increment value in MySQL in various ways. The first way is preferable because it is the easiest way and has no side effects.