This is a summary of a Wikipedia article. It specifies the different types of relationships you can stipulate in PHPmyadmin. I am putting it here because it is relevant to @Nathan’s comment on setting the foreign keys options for “on update/delete” but is too large for a comment – hope it helps.
Whenever rows in the master (referenced) table are deleted (resp. updated), the respective rows of the child (referencing) table with a matching foreign key column will get deleted (resp. updated) as well. This is called a cascade delete (resp. update).
A value cannot be updated or deleted when a row exists in a foreign key table that references the value in the referenced table. Similarly, a row cannot be deleted as long as there is a reference to it from a foreign key table.
NO ACTION and RESTRICT are very much alike. The main difference between NO ACTION and RESTRICT is that with NO ACTION the referential integrity check is done after trying to alter the table. RESTRICT does the check before trying to execute the UPDATE or DELETE statement. Both referential actions act the same if the referential integrity check fails: the UPDATE or DELETE statement will result in an error.
The foreign key values in the referencing row are set to NULL when the referenced row is updated or deleted. This is only possible if the respective columns in the referencing table are nullable. Due to the semantics of NULL, a referencing row with NULLs in the foreign key columns does not require a referenced row.
Similar to SET NULL, the foreign key values in the referencing row are set to the column default when the referenced row is updated or deleted.
注意点：两张表都必须是Inno DB引擎。referencing field必须创建索引。