Question

I have a table that is close to 20million records and growing. The table was setup as innodb. There is a primary index on the two main fields:

`entries_to_fields`
entry_id    int(11) NO  PRI NULL     
field_id    int(11) NO  PRI NULL     
value   text    NO      NULL     

Despite the number of records, most of the queries to this table are exceptionally quick, except for the following:

DELETE FROM `entries_to_fields` WHERE `entry_id` IN (SELECT `id` FROM `entries` WHERE `form_id` = 196)

This deletes all entry data for a specific form.

Currently this is taking over 45 seconds, even if the entries table returns no results.

My question is can is there a simple change to the entries_to_fields structure I can make, or can I optomise my query further.

Answer 1

After I read your answer, I wrote this query that may help you as well (in future).

DELETE entries_to_fields
FROM entries_to_fields
JOIN entries
ON entries_to_fields.entry_id = entries.id
WHERE entries.form_id = 196

… entries.form_id field should be indexed.