在MySQL中无限制地强制执行删除级联

Question

I'd like to know if it's possible to force a cascade when deleting in MySQL?

I know that a in order to be able to delete all the childs of a parent this has to exists:

REFERENCES table (fk) ON DELETE CASCADE ON UPDATE CASCADE

But my tables doesn't have it, so, back to my question, is there a way to force it?

Answer 1

One either puts it in the original table creation, or attempts to establish it after the fact with ALTER TABLE

mysql Manual Page on ALTER TABLE Syntax

If one chooses to establish after the fact, the same rules apply as seen in the above link. Failing those or data pre-existing such that the enforcement will fail with the ALTER TABLE call, then the attempt will fail to establish the fk with a cascading delete.

See that manual page, and look into ADD CONSTRAINT and DROP CONSTRAINT . There is no altering of an existing constraint. Rather one must drop it then re-add it.

An alter add example"

ALTER TABLE lunches
ADD CONSTRAINT `fk_lunches_users`
FOREIGN KEY (`studentId` )
REFERENCES `students` (`studentId` )
ON DELETE CASCADE;

Also of interest is foreign_key_checks that should be investigated. That is, is one willing to temporarily disable them.