Maciek,
>Hi,
>
>Is this correct for MySQL to increment the auto_increment counter if the
>INSERT query fails? For example:
>
>mysql> CREATE TABLE test ( i INT NOT NULL AUTO_INCREMENT, c CHAR(16) NOT
>NULL, PRIMARY KEY(i), UNIQUE(c)) type=InnoDB;
>Query OK, 0 rows affected (0.25 sec)
>
>mysql> INSERT INTO test VALUES('', 'test1');
>Query OK, 1 row affected (0.05 sec)
>
>mysql> INSERT INTO test VALUES('', 'test2');
>Query OK, 1 row affected (0.24 sec)
>
>mysql> INSERT INTO test VALUES('', 'test2');
>ERROR 1062: Duplicate entry 'test2' for key 2
>mysql> INSERT INTO test VALUES('', 'test3');
>Query OK, 1 row affected (0.02 sec)
>
>mysql> SELECT * FROM test;
>+---+-------+
>| i | c |
>+---+-------+
>| 1 | test1 |
>| 2 | test2 |
>| 4 | test3 |
>+---+-------+
>3 rows in set (0.00 sec)
auto-inc values are assigned past the transactional mechanism, for
efficiency, and to avoid deadlocks. Therefore a rollback following a failing
insert statement does not roll back the counter.
If you want a strictly contiguous sequence of values, use the standard
technique of a counter row in another table, from which you assign the
values to your insert statements.
CREATE TABLE test_counter(a INT) TYPE = INNODB;
SELECT a FROM testcounter FOR UPDATE;
UPDATE testcounter SET a = a + 1;
INSERT INTO test (...);
Regards,
Heikki
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