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MySQL "on delete cascade" doesn't appear to work.

After I set up a test database:

CREATE TABLE hit (
id int(10) unsigned NOT NULL auto_increment,
visitorId int(10) unsigned NOT NULL,
PRIMARY KEY (id),
KEY visitorId (visitorId)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO hit (id, visitorId) VALUES
(1, 1),
(2, 2),
(3, 3);

CREATE TABLE visitor (
id int(10) unsigned NOT NULL auto_increment,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO visitor (id) VALUES
(1),
(2),
(3);

ALTER TABLE hit ADD FOREIGN KEY (visitorId) REFERENCES visitor(id) ON DELETE CASCADE;

I get:

mysql> select * from hit;
+----+-----------+
| id | visitorId |
+----+-----------+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
+----+-----------+
3 rows in set (0.00 sec)

mysql> select * from visitor;
+----+
| id |
+----+
| 1 |
| 2 |
| 3 |
+----+
3 rows in set (0.00 sec)

When I:

mysql> delete from hit where id=2;
Query OK, 1 row affected (0.00 sec)

mysql> select * from hit;
+----+-----------+
| id | visitorId |
+----+-----------+
| 1 | 1 |
| 3 | 3 |
+----+-----------+
2 rows in set (0.00 sec)

mysql> select * from visitor;
+----+
| id |
+----+
| 1 |
| 2 |
| 3 |
+----+
3 rows in set (0.00 sec)

The delete doesn't cascade to the visitor table. Why not?

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philipjonathan

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arantius

ASKER

I see. So, if it's not obvious, I'm recording hits to web pages. Each hit references multiple separate values like the URL, the visitor that made it, and so forth. I periodically throw away old hit records (in this case, I'm only interested in about the past week at any time), and I was hoping to use cascade to automatically discard e.g. visitors that don't have any hit records left.

Is there a straightforward way to do this?

philipjonathan

Well, I don't think we can use on delete cascade here. Probably what you can do is to periodically check the visitor table and delete records which don't have child records.

MySQL &quot;on delete cascade&quot; doesn't appear to work.

MySQL "on delete cascade" doesn't appear to work.