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Mysql can parse the foreign key syntax for the myisam table type (meaning no error message will be raised if it encounters an fk definition), making migration from other database products or table engines easier because you do not have to edit the create table statements to remove them.
the problem is most likely that questions.p_id and users.p_id are not defined as INT NOT NULL. for foreign keys to work, the definition of the columns on both side of the foreign key must match exactly, with the exception of auto_increment and default.
1.7.2.3 FOREIGN KEY Constraint Differences. The MySQL implementation of foreign key constraints differs from the SQL standard in the following key respects: If there are several rows in the parent table with the same referenced key value, InnoDB performs a foreign key check as if the other parent rows with the same key value do not exist.
28 lis 2019 · I need to migrate a lot of mysql MyISAM table to a new InnoDb version, adding foreign key constraints. I can dump and import, disabling first foreign key checks. But is there a way to check which tables have constraint problems (without checking manually all of them) when I activate again the foreign key check?
The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables. A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table.
The MATCH clause in the SQL standard controls how NULL values in a composite (multiple-column) foreign key are handled when comparing to a primary key in the referenced table. MySQL essentially implements the semantics defined by MATCH SIMPLE, which permits a foreign key to be all or partially NULL. In that case, a (child table) row containing ...
MySQL supports foreign key references between one column and another within a table. (A column cannot have a foreign key reference to itself.) In these cases, a “ child table record ” refers to a dependent record within the same table.
