MySQL delete across multiple tables - php

Question

I am working on a cron script (in PHP PDS for a MySQL db) that will delete data older than 30 days from the database. Ive tried to do joining and on delete cascaded on my tables and statements but they haven't worked out so I went with a simpler approach here to get it working however I know this isn't the most processor effective method.
Please note that some of these tables (especially the links table) have hundreds of thousands of rows so that's why I wanted to be a little more clever than what I have here.
The table structure is easy, there is a table key table that has a time stamp and an id. That id is repeated in all tables as tablekey_id.
My current cron job is as follows.
/* Cron script to delete old data from the database. */
if (#include dirname(dirname(dirname(__FILE__))) . '/dbconn/website_connections.php') {
$conn = $connectionFromOtherFile;
$keyTable = 'table_key';
$linksTable = 'links';
$domainsTable = 'link_domains';
$terms = 'searched_domains';
$query = $conn->query("SELECT `id` FROM `$keyTable` WHERE `timestamp` < (NOW() - INTERVAL 30 DAY)");
$query->setFetchMode(PDO::FETCH_ASSOC);
while($row = $query->fetch()) {
$conn->exec("DELETE FROM `$linksTable` WHERE `tablekey_id` = $row[id]");
$conn->exec("DELETE FROM `$domainsTable` WHERE `tablekey_id` = $row[id]");
$conn->exec("DELETE FROM `$terms` WHERE `tablekey_id` = $row[id]");
$conn->exec("DELETE FROM `$keyTable` WHERE `id` = $row[id]");
}
}
Is there any way to get this into one statement? Please and thank you for the assistance.
EDIT: Heres what I ended up with.
/* Cron script to delete old data from the database. */
if (#include dirname(dirname(dirname(__FILE__))) . '/dbconn/website_connections.php') {
$conn = $connectionFromOtherFile;
$keyTable = 'table_key';
$linksTable = 'links';
$domainsTable = 'link_domains';
$terms = 'searched_domains';
$delete = $conn->prepare("DELETE tablekey, linktable, domaintable, searched
FROM `$keyTable` AS tablekey
LEFT OUTER JOIN `$linksTable` AS linktable on tablekey.id = linktable.tablekey_id
LEFT OUTER JOIN `$domainsTable` AS domaintable on tablekey.id = domaintable.tablekey_id
LEFT OUTER JOIN `$terms` AS searched on tablekey.id = searched.tablekey_id
WHERE tablekey.id = :tablekey_id");
$query = $conn->query("SELECT `id` FROM `$keyTable` WHERE `timestamp` < (NOW() - INTERVAL 30 DAY)");
$query->setFetchMode(PDO::FETCH_ASSOC);
while($row = $query->fetch()) {
$delete->execute(array('tablekey_id' => $row['id']));
}
}

Answer 1

You should be able to delete with one query like this:
DELETE kt, lt, dt, t
FROM `$keyTable` AS kt
LEFT OUTER JOIN `$linksTable` AS lt on kt.id = lt.tablekey_id
LEFT OUTER JOIN `$domainsTable` AS dt on kt.id = dt.tablekey_id
LEFT OUTER JOIN `$terms` AS t on kt.id = t.tablekey_id
WHERE kt.id = $row[id]
Note that I used outer joins here as I wasn't sure if the tables other than keyTable would be guaranteed to have records with that tablekey_id. If they are, you could use an inner join.

Answer 2

If tablekey_id is indexed, this should be fine even with thousands of rows. If you want to keep your database schema simple, I would keep 4 queries, deleting is not that CPU intensive.
If you really want one statement, you will have to complicate things and use a cascading deletion with foreign keys constraints:
CASCADE: Delete or update the row from the parent table, and automatically delete or update >the matching rows in the child table. Both ON DELETE CASCADE and ON UPDATE CASCADE are supported. Between two tables, do not define several ON UPDATE CASCADE clauses that act on the same column in the parent table or in the child table.
Source: http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html
And this is admitting that your database is innoDB

Answer 3

first you want to retrieve the list of IDs like you are doing now, then you want to construct 4 queries like this:
DELETE FROM 'table' where 'id' IN ('id1', 'id2', 'id4')
this should prove a LOT more efficient then doing separate deletes. It would reduce the amount of queries to 5 in stead of 1+ 4N

Answer 4

As far as I know PDO only accepts one statement...
You could look at a trigger on deleting from the first (or you're main) table...

Answer 5

Sometimes I use this to solve my problems. Put the ids in string first.
$ids = array();
while($row = $query->fetch()) {
$ids[] = $row[id];
}
$ids_str = implode(',', $ids);
$conn->exec("DELETE FROM `$linksTable` WHERE `tablekey_id` in ($ids_str) ");
$conn->exec("DELETE FROM `$domainsTable` WHERE `tablekey_id` in ($ids_str)");
$conn->exec("DELETE FROM `$terms` WHERE `tablekey_id` in ($ids_str)");
$conn->exec("DELETE FROM `$keyTable` WHERE `id` in ($ids_str)");