1. yes indexes could help, if mysql uses them. The mysql optimiser may or may not use the index for the query depending on the statement...it sounds like you are doing a full table scan on the data

2. there are two schools of thought here:
a. run the whole thing as two statements (one outer loop to loop thru the course list, and an inner one to get the attendees) b. examine the join query to see if you are starting out in the correct way (mysql can be sensitive to the way the tables are joined), examine the indexes and use the EXPLAIN statement to see how the optimiser attempts the query.


I would just test both ways and see which one performs better...

Bastien


From: Tony Grimes <[EMAIL PROTECTED]>
To: PHP-DB <php-db@lists.php.net>
Subject: [PHP-DB] SQL Performance Help
Date: Wed, 27 Dec 2006 14:05:13 -0700

I'm developing a course calendar for a client and I'm running into
performance problems with the admin site. For example, when I try to include registration counts in the course list, the page really slows down for large
course lists (50 or so):

COURSE        ATTENDEES      CAPACITY    SEATS LEFT
======        =========      ========    ==========
Course 1         5              10           5
Course 2         6              15           9
Course 3         4              10           6

I've been using one query to retrieve the course list and then one for each
attendee count. Is there a more efficient way of doing this all in one
query? I was thinking something like this (I'm not a SQL expert, so I don't
know if this is even possible):

SELECT
    course_name,
    capacity,
    count(query here) as attendee_count
FROM events AS e
LEFT OUTER JOIN event_attendees AS a ON e.event_id = a.event_id
WHERE start_time BETWEEN point_a AND point_b

Or should I just pull everything as a separate row like this and sort it all
out programmatically:

SELECT
    e.course_name,
    e.capacity,
    a.user_id
FROM events AS e
LEFT OUTER JOIN event_attendees AS a ON e.event_id = a.event_id
WHERE start_time BETWEEN point_a AND point_b

Or should I just try caching the data in PHP? Would an index help?

I realize any answers might be complicated, but if you could just point me
in the right direction, I can probably figure the rest out.

Thanks,
Tony

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