MySQL Trigger: Delete From Table AFTER DELETE

Question

Scope: Two tables. When a new patron is created, they have some information about them stored into a 2nd table (This was done using a trigger as well, it works as expected). Here's an example of my table structure and relationship.

Table 1-> patrons

+-----+---------+-----+
+  id +   name  + val +
+=====+=========+=====+
+  37 +  george +  x  +
+-----+---------+-----+
+  38 +  sally  +  y  +
+-----+---------+-----+

Table 2 -> patron_info

+----+-----+----------+
+ id + pid +   name   +
+----+-----+----------+
+  1 +  37 +  george  +
+----+-----+----------+
+  2 +  38 +  sally   +
+----+-----+----------+

The administrator can manage the patrons. When they choose to remove a patron, the patron is removed from the table 1 patrons . At this point, nothing happens to table 2 patron_info .

I'm simply trying to create a trigger to delete from table 2, when table 1 has an item deleted. Here's what I've tried...

Initially, I try to drop the trigger if it exists (just to clear the air)...

DROP TRIGGER IF EXISTS log_patron_delete;

Then I try to create the trigger afterwards...

CREATE TRIGGER log_patron_delete AFTER DELETE on patrons
FOR EACH ROW
BEGIN
DELETE FROM patron_info
    WHERE patron_info.pid = patrons.id
END

At this point, I get a syntax error 1046: Check syntax near END on line 6 . I don't know what the error is at this point. I've tried several different variations. Also, am I required to use a delimiter here?

Can anyone help restore my sanity?

Answer 1

I think there is an error in the trigger code. As you want to delete all rows with the deleted patron ID, you have to use old.id (Otherwise it would delete other IDs)

Try this as the new trigger:

CREATE TRIGGER log_patron_delete AFTER DELETE on patrons
FOR EACH ROW
BEGIN
DELETE FROM patron_info
    WHERE patron_info.pid = old.id;
END

Dont forget the ";" on the delete query. Also if you are entering the TRIGGER code in the console window, make use of the delimiters also.

Answer 2

为什么不在外键patron_info .pid 上设置ON CASCADE DELETE？

Answer 3

create trigger doct_trigger
after delete on doctor
for each row
delete from patient where patient.PrimaryDoctor_SSN=doctor.SSN ;