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3.6.9. Using AUTO_INCREMENT

The AUTO_INCREMENT attribute can be used to generate a unique identity for new rows: 

CREATE TABLE animals (
     id MEDIUMINT NOT NULL AUTO_INCREMENT,
     name CHAR(30) NOT NULL,
     PRIMARY KEY (id)
) ENGINE=MyISAM;

INSERT INTO animals (name) VALUES
    ('dog'),('cat'),('penguin'),
    ('lax'),('whale'),('ostrich');

SELECT * FROM animals;

Which returns: 

+----+---------+
| id | name    |
+----+---------+
|  1 | dog     |
|  2 | cat     |
|  3 | penguin |
|  4 | lax     |
|  5 | whale   |
|  6 | ostrich |
+----+---------+

No value was specified for the AUTO_INCREMENT column, so MySQL assigned sequence numbers automatically. You can also explicitly assign NULL or 0 to the column to generate sequence numbers.

You can retrieve the most recent AUTO_INCREMENT value with the LAST_INSERT_ID() SQL function or the mysql_insert_id() C API function. These functions are connection-specific, so their return values are not affected by another connection which is also performing inserts.

Use a large enough integer data type for the AUTO_INCREMENT column to hold the maximum sequence value you will need. When the column reaches the upper limit of the data type, the next attempt to generate a sequence number fails. For example, if you use TINYINT, the maximum permissible sequence number is 127. For TINYINT UNSIGNED, the maximum is 255.

Note

For a multiple-row insert, LAST_INSERT_ID() and mysql_insert_id() actually return the AUTO_INCREMENT key from the first of the inserted rows. This enables multiple-row inserts to be reproduced correctly on other servers in a replication setup.

For MyISAM and BDB tables you can specify AUTO_INCREMENT on a secondary column in a multiple-column index. In this case, the generated value for the AUTO_INCREMENT column is calculated as MAX(auto_increment_column) + 1 WHERE prefix=given-prefix. This is useful when you want to put data into ordered groups. 

CREATE TABLE animals (
    grp ENUM('fish','mammal','bird') NOT NULL,
    id MEDIUMINT NOT NULL AUTO_INCREMENT,
    name CHAR(30) NOT NULL,
    PRIMARY KEY (grp,id)
) ENGINE=MyISAM;

INSERT INTO animals (grp,name) VALUES
    ('mammal','dog'),('mammal','cat'),
    ('bird','penguin'),('fish','lax'),('mammal','whale'),
    ('bird','ostrich');

SELECT * FROM animals ORDER BY grp,id;

Which returns: 

+--------+----+---------+
| grp    | id | name    |
+--------+----+---------+
| fish   |  1 | lax     |
| mammal |  1 | dog     |
| mammal |  2 | cat     |
| mammal |  3 | whale   |
| bird   |  1 | penguin |
| bird   |  2 | ostrich |
+--------+----+---------+

In this case (when the AUTO_INCREMENT column is part of a multiple-column index), AUTO_INCREMENT values are reused if you delete the row with the biggest AUTO_INCREMENT value in any group. This happens even for MyISAM tables, for which AUTO_INCREMENT values normally are not reused.

If the AUTO_INCREMENT column is part of multiple indexes, MySQL will generate sequence values using the index that begins with the AUTO_INCREMENT column, if there is one. For example, if the animals table contained indexes PRIMARY KEY (grp, id) and INDEX (id), MySQL would ignore the PRIMARY KEY for generating sequence values. As a result, the table would contain a single sequence, not a sequence per grp value.

To start with an AUTO_INCREMENT value other than 1, you can set that value with CREATE TABLE or ALTER TABLE, like this: 

mysql> ALTER TABLE tbl AUTO_INCREMENT = 100;

More information about AUTO_INCREMENT is available here:

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User Comments

Posted by Guy Martin on June 19 2003 3:50pm[Delete] [Edit]

For those that are looking to "reset" the auto_increment, say on a list that has had a few deletions and you want to renumber everything, you can do the following.

DROP the field you are auto_incrementing.
ALTER the table to ADD the field again with the same attributes.

You will notice that all existing rows are renumbered and the next auto_increment number will be equal to the row count plus 1.

(Keep in mind that DROPping that column will remove all existing data, so if you have exterior resources that rely on that data, or the numbers that are already there, you may break the link. Also, as with any major structure change, it's a good idea to backup your table BEFORE you make the change.)

Posted by [name withheld] on June 22 2003 4:19pm[Delete] [Edit]

In order to reset the auto_increment, in a situation where some of the most recently added rows were deleted, use:

ALTER TABLE theTableInQuestion AUTO_INCREMENT=1234

and future insertions will be numbered from 1234 again (unless you still had rows numbered greater than 1234, and then the future insertions will start from the greatest number + 1 ).

Posted by [name withheld] on October 23 2003 8:41pm[Delete] [Edit]

The manual should probably make *better* mention of the fact that the order in which primary keys are specified determines the semantics by which a new value is selected. (Saying "... is calculated as MAX(auto_increment_column)+1) WHERE prefix=given-prefix." is unclear given that this is the first mention of the word "prefix" in the document.

For example,

create table location
(
id bigint not null auto_increment, -- "serial" per 4.1
longitude int,
latitude int,
place int,
primary key(id, longitude, latitude, place)
);

insert into location (longitude, latitude, place)
values (0,0,0), (1,1,1), (2,2,2);

select * from foo;

+----+-----------+----------+-------+
| id | longitude | latitude | place |
+----+-----------+----------+-------+
|  1 |         0 |        0 |     0 |
|  2 |         1 |        1 |     1 |
|  3 |         2 |        2 |     2 |
+----+-----------+----------+-------+

drop table location;

create table location
(
id bigint not null auto_increment, -- "serial" per 4.1
longitude int,
latitude int,
place int,
primary key(longitude, latitude, place, id)
);

insert into location (longitude, latitude, place)
values (0,0,0), (1,1,1), (2,2,2), (0,0,0);

select * from location order by id;
+----+-----------+----------+-------+
| id | longitude | latitude | place |
+----+-----------+----------+-------+
|  1 |         0 |        0 |     0 |
|  1 |         1 |        1 |     1 |
|  1 |         2 |        2 |     2 |
|  2 |         0 |        0 |     0 |
+----+-----------+----------+-------+

Unless I've misunderstood (please correct me if I'm wrong), it's a nice feature but should be better documented than it is.

Thanks,

jrl.

Posted by [name withheld] on November 8 2004 8:35pm[Delete] [Edit]

Drop table command will also reset autoincrement

Posted by nav on February 7 2006 7:56am[Delete] [Edit]

reset auto_increment using....

alter table "table_name" auto_increment=1
resets auto_increment to 1 + max(auto_increment)

Posted by kernel panic on March 24 2008 5:25am[Delete] [Edit]

Another way to get the next Auto_increment value is using the information_schema:

SELECT Auto_increment FROM information_schema.tables WHERE table_name='the_table_you_want';

Posted by Gabe Holmes on July 12 2009 9:41pm[Delete] [Edit]

If you're using a phpmyadmin, go to the table in question and then Operations->Table Options->Auto-Increment
Set the auto-increment to whatever you please.

Remember to check any foreign keys before doing anything serious, brush your teeth every day and wear sunscreen at the beach.

Posted by Lewis Graham on August 26 2009 5:54am[Delete] [Edit]

InnoDB resets the next auto_increment value to the highest value in the table + 1 after a server restart.
This means that if you delete the highest value(s) in the table, then restart you can get the same values for auto_increment again.
See: http://bugs.mysql.com/bug.php?id=727

Posted by Luke Up on March 7 2011 11:15pm[Delete] [Edit]

To reset auto_increment to 1, first make a backup of your table. I usually make 2 backups by copying my table 2 times (different names). Using one of the copies, delete the auto_increment field. Then run - ALTER TABLE `table_name` ADD `auto_increment_field` INT( 6 ) NOT NULL AUTO_INCREMENT FIRST, ADD PRIMARY KEY ( `auto_increment_field` ); If it works, Rename the original table to table_save and rename your modified table to the original table. Tested on phpmyadmin and mysql cli. Hope this helps.

Posted by Daniel Bartley on June 29 2011 1:40am[Delete] [Edit]

-- Usage:
-- ResetTableIdentities('your_table_name');
-- Description:
-- Resets the Auto_Increment of the table [your_table_name] only when the number of rows in the [your_table_name] is equal to 0

DELIMITER $$

CREATE DEFINER=`root`@`%` PROCEDURE `ResetTableIdentities`(IN table_name VARCHAR(64))
BEGIN
SET @returned_row_count = 0;
SET @table_name = table_name;

SET @statement = CONCAT("SELECT COUNT(*) INTO @returned_row_count FROM ", @table_name, ";");
PREPARE stmt FROM @statement;
EXECUTE stmt;

IF (@returned_row_count = 0) THEN
SET @statement2 = CONCAT("ALTER TABLE ", @table_name, " AUTO_INCREMENT = 1;");
PREPARE stmt2 FROM @statement2;
EXECUTE stmt2;

DEALLOCATE PREPARE stmt2;
END IF;
DEALLOCATE PREPARE stmt;
END

Posted by Sohail Khurshid on August 8 2011 11:15am[Delete] [Edit]

What's the point of mentioning such huge 'workarounds' when the auto_increment reset issue can be resolved simply by: "alter table "table_name" auto_increment=1" (as a couple of other people suggested too)?

Posted by Thomas Mayer on January 20 2012 3:17pm[Delete] [Edit]

As InnoDb forgets its highest auto_increment after server restart, you can set it again, if you have stored it anywhere. This happens often if you archive your data in an archive table and then delete it and then restart mysql. When archiving again this will result in duplicate key entries.

To work around this you can create a trigger which makes sure your auto_increment is higher than the auto_increment of your archive table:

delimiter //
drop trigger if exists trigger_autoinc_tbl;
CREATE TRIGGER trigger_autoinc_tbl BEFORE INSERT ON tbl
FOR EACH ROW
BEGIN
declare auto_incr1 BIGINT;
declare auto_incr2 BIGINT;
SELECT AUTO_INCREMENT INTO auto_incr1 FROM information_schema.TABLES WHERE table_schema=DATABASE() AND table_name='tbl';
SELECT AUTO_INCREMENT INTO auto_incr2 FROM information_schema.TABLES WHERE table_schema=DATABASE() AND table_name='tbl_archiv';
IF (auto_incr2 > auto_incr1 and NEW.id<auto_incr2) THEN
SET NEW.id = auto_incr2;
END IF;
END;//
delimiter ;

Further reading: http://www.slicewise.net/index.php?id=82

Posted by Anil Purushothaman on October 10 2012 8:37am[Delete] [Edit]

When using MySQL Workbench, you can reset the auto increment to 1 as follows -
Step 1 : In SQL Editor window, right click on the table name containing the auto increment field and select "Alter Table..."
Step 2 : Select "options" table in the alter table window pane.
Step 3 : The Auto Increment field here shows the current value that it has reached. Simply change it to the value you want (1 in this case).
Step 4 : Apply and close.

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