In what order are ON DELETE CASCADE constraints processed?

Question

Here is an example of what I\'ve got going on:

CREATE TABLE Parent (id BIGINT NOT NULL,
  PRIMARY KEY (id)) ENGINE=InnoDB;

CREATE TABLE Child (id BIGINT NOT         


        

Answer 1

The parent deletion is triggering the child deletion as you stated and I don't know why it goes to the child table before the uncle table. I imagine you would have to look at the dbms code to know for sure, but im sure there is an algorithm that picks which tables to cascade to first.

The system does not really 'figure out' stuff the way you imply here and it is just following its constraint rules. The problem is the schema you created in that it encounters a constraint that will not let it pass further.

I see what you are saying.. if it hit the uncle table first it would delete the record and then delete the child (and not hit the uncle cascade from the child deletion). But even so, I don't think a schema would be set up to rely on that kind of behavior in reality. I think the only way to know for sure what is going on is to look through the code or get one of the mysql/postgresql programmers in here to say how it processes fk constraints.