Subquery Slows Query down significantly - mysql

Question

I'm trying to do a query that replaces multiple queries to produce a result set. I've got a fairly straight forward set of 1 to 1 joins, but one column I'm trying to get from a table that keeps multiple records per primary record. Basically it's like this:
meet_entries with a primary key id column and a bunch of other columns,
meet_entries_statuses, with an autoincrement id column and a foreign key to the id column of meet_entry
There may be multiple rows in meet_entry_statuses for each row in meet_entries. In my query, I'm trying to get the most recently added(so highest id number) row associated with the meet_entry primary key id.
Here's my query:
SELECT
meet_entries.id,
member.firstname,
member.surname,
member.gender,
member.dob,
clubs.code,
clubs.clubname,
meet_entries.meals,
meet_entries.massages,
meet_entries.cost,
meet_entries.cancelled,
(SELECT meet_entry_status_codes.description
FROM meet_entry_statuses, meet_entry_status_codes
WHERE meet_entry_statuses.code = meet_entry_status_codes.id
AND meet_entry_statuses.id = meet_entries.id
ORDER BY meet_entry_statuses.id DESC
LIMIT 1) as status,
COUNT(DISTINCT meet_events_entries.id) as entries
FROM meet_entries, meet_events_entries, member, clubs, meet_entry_statuses, meet_entry_status_codes
WHERE meet_entries.meet_id = ?
AND meet_entries.id = meet_events_entries.meet_entry_id
AND meet_entries.member_id = member.id
AND meet_entries.club_id = clubs.id
GROUP BY meet_entries.id
;
Adding the bit:
(SELECT meet_entry_status_codes.description
FROM meet_entry_statuses, meet_entry_status_codes
WHERE meet_entry_statuses.code = meet_entry_status_codes.id
AND meet_entry_statuses.id = meet_entries.id
ORDER BY meet_entry_statuses.id DESC
LIMIT 1) as status,
takes the query from being .2 of a second, to never finishing. There are only 10 matching rows in meet_entries. There are about 50 rows in the meet_entries_statuses appropriate to the 10 rows in meet_entries, but as I say I'm trying to only get 1 row for each meet_entries row. Any suggestions on a better way to do this?

Answer 1

I am not very sure why you would join with meet_entry_statuses and meet_entry_status_codes without any join conditions. Doing so means that you are doing a cross join. So if there are N rows in meet_entries, and M and P rows in the above two tables respectively, you end up generating N x M x P rows.
Can you try taking out the two joins. I marked them out in the following rewritten query:
SELECT
meet_entries.id,
member.firstname,
member.surname,
member.gender,
member.dob,
clubs.code,
clubs.clubname,
meet_entries.meals,
meet_entries.massages,
meet_entries.cost,
meet_entries.cancelled,
(SELECT
meet_entry_status_codes.description
FROM
meet_entry_statuses as mes
, meet_entry_status_codes as mesc
WHERE
meet_entry_statuses.code = meet_entry_status_codes.id
AND meet_entry_statuses.id = meet_entries.id
ORDER BY meet_entry_statuses.id DESC
LIMIT 1
) as status,
COUNT(DISTINCT meet_events_entries.id) as entries
FROM
meet_entries as me
, meet_events_entries as mee
, member as m
, clubs as c
, meet_entry_statuses as mes -- try taking this out
, meet_entry_status_codes as mesc -- try taking this out
WHERE
meet_entries.meet_id = ?
AND meet_entries.id = meet_events_entries.meet_entry_id
AND meet_entries.member_id = member.id
AND meet_entries.club_id = clubs.id
GROUP BY meet_entries.id
;