Description of MySQL InnoDB foreign key constraints

• Cascade:
  Deletes or updates matched rows from the parent table and automatically deletes or updates the child table. On Delete cascade and on update cascade are both available. Between two tables, you should not define several on update cascade clauses that take actions in the same column of the parent or child table.
• Set NULL:
  Delete or update rows from the parent table, and set the foreign key column in the child table to null. If the foreign key column does not specify the not null qualifier, this is unique and valid. The on Delete set null and on update set null clauses are supported.
• No action:
  In ANSI SQL-92 standards, no action means this does not take action, that is, if there is a related foreign key value in the referenced table, attempts to delete or update key values are not allowed (Gruber, Master SQL, 2000: 181 ). InnoDB rejects the deletion or update operation on the parent table.
• Restrict:
  The deletion or update of the parent table is denied. No action and restrict are both the same. delete on
  Delete or on update clause. (Some database systems have extended checks and no
  Action is an extension check. In MySQL, foreign key constraints are checked immediately, so no action and restrict are the same ).
• Set default:
  This action is parsedProgramBut InnoDB rejects table definitions that contain the on Delete set default or on update set default clause.