5.4.5. InnoDB and FOREIGN KEY Constraints

This section describes differences in the InnoDB storage engine' handling of foreign keys as compared with that of the MySQL Server.

Foreign Key Definitions

Foreign key definitions for InnoDB tables are subject to the following conditions:

Referential Actions

Referential actions for foreign keys of InnoDB tables are subject to the following conditions:

Foreign Key Usage and Error Information

You can obtain general information about foreign keys and their usage from querying the INFORMATION_SCHEMA.KEY_COLUMN_USAGE table, and more information more specific to InnoDB tables can be found in the INNODB_SYS_FOREIGN and INNODB_SYS_FOREIGN_COLS tables, also in the INFORMATION_SCHEMA database. See also Section, "Using FOREIGN KEY Constraints".

In addition to SHOW ERRORS, in the event of a foreign key error involving InnoDB tables (usually Error 150 in the MySQL Server), you can obtain a detailed explanation of the most recent InnoDB foreign key error by checking the output of SHOW ENGINE INNODB STATUS.

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