How To Set Auto_increment In Mysql After Creating Table

Summary: in this tutorial, we will show you various ways to reset 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 namedtmp and assign theAUTO_INCREMENT attribute to theid primary key column.

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

Code language: SQL (Structured Query Language) ( sql )

Second, insert some sample data into the tmp table:

                                          INSERT                INTO                tmp(name)                VALUES('test 1'),       ('test 2'),       ('test 3');            
                          Code language:              SQL (Structured Query Language)              (              sql              )

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

                                          SELECT                *                FROM                tmp;            
                          Code language:              SQL (Structured Query Language)              (              sql              )

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

Using 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;

Code language: SQL (Structured Query Language) ( sql )

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;

Code language: SQL (Structured Query Language) ( sql )

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

ALTER TABLE tmp AUTO_INCREMENT = 3;

Code language: SQL (Structured Query Language) ( sql )

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;            
                          Code language:              SQL (Structured Query Language)              (              sql              )

MySQL Reset Auto-Increment Value Example

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

Using 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;

Code language: SQL (Structured Query Language) ( sql )

By using the TRUNCATE TABLE 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 delete all data from the table permanently.

Like the TRUNCATE TABLE 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(...);

Code language: SQL (Structured Query Language) ( sql )

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

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