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.
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