[MDEV-9790] MyISAM allows AUTO_INCREMENT columns with no index - Jira

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This script:

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a CHAR(20) NOT NULL, b INT NOT NULL AUTO_INCREMENT, INDEX(a,b)) ENGINE=InnoDB;

correctly return an error:

ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key

If I now change ENGINE to MyISAM, it creates the table with no errors:

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a CHAR(20) NOT NULL, b INT NOT NULL AUTO_INCREMENT, INDEX(a,b)) ENGINE=MyISAM;

INSERT INTO t1 (a) VALUES ('a'),('b'),('c');

SELECT * FROM t1;

but AUTO_INCREMENT does not actually work:

+---+---+

| a | b |

+---+---+

| a | 1 |

| b | 1 |

| c | 1 |

+---+---+

The problem seems to be introduced by:

Author: unknown <monty@mashka.mysql.fi>  2003-03-07 14:36:52

Committer: unknown <monty@mashka.mysql.fi>  2003-03-07 14:36:52

    Fixed AUTO_INCREMENT handling in MyISAM (last auto_increment patch broke things)

    Some after merge fixes

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