MySQL - Multirow Sum without Subquery - mysql

Question

I currently have this working using a Sub-query, but as the DB grows this will become HUGELY inefficient. I'm wondering if there is a more efficient way to do what I need to do without sub-queries?
I need to have my final output look like so:
Question, Answer, Responses, Charts included in Response Count
Did this work?, N/A, 26, 30
Did this work?, Yes, 4, 30
This is my current query:
SELECT
bq_text,
ba_a,
bq_id,
COUNT(ba_a) AS ba_aC,
(SELECT COUNT(*) FROM board_done_sheet WHERE sd_b_id = bs.bs_id AND sd_sub = 1) AS sd_chartnumC
FROM board_done_sheet AS sh
LEFT JOIN board_done bd
ON (bd.bd_id = sh.sd_bd_id)
LEFT JOIN boardsubs bs
ON (bd.bd_b_id = bs.bs_id)
LEFT JOIN b_q_answers ba
ON (sh.sd_s_id = ba.ba_s_id)
LEFT JOIN bsquestions bq
ON (bq.bq_id = ba.ba_q_id)
LEFT JOIN multiples m
ON (ba.ba_m_id = m.m_id)
LEFT JOIN users u
ON (u.us_id = bd.bd_d_id)
LEFT JOIN profiles p
ON (p.p_u_id = bd.bd_d_id)
LEFT JOIN users rev
ON (rev.us_id = bd.bd_rev)
WHERE sd_sub = '1' AND bq_text <> 'Date' AND bq_id = 380
GROUP BY bs_id, bq_text, ba_a
That works perfectly, the problem is it has to use sub-queries which as time goes by will get less efficient.
I'm just wondering if there is a better more efficient way to do that summed field without it.

Answer 1

Presumably the subquery you're concerned about is the one in your toplevel SELECT.
That is easy to refactor so it won't get repeated.
Just JOIN it to the rest of the table. You'll want this sort of thing:
SELECT
bq_text, ...
COUNT(ba_a) AS ba_aC,
countup.countup AS sd_chartnumC
FROM board_done_sheet AS sh
LEFT JOIN board_done bd
ON (bd.bd_id = sh.sd_bd_id)
...
LEFT JOIN users rev
ON (rev.us_id = bd.bd_rev)
JOIN (
SELECT COUNT(*) AS countup , sd_b_id
FROM board_done_sheet
WHERE sd_sub = 1
GROUP BY sd_b_id
) AS countup ON countup.sd_b_id = bs.bs_id
WHERE sd_sub = '1'
AND bq_text <> 'Date'
AND bq_id = 380
GROUP BY bs_id, bq_text, ba_a
The countup subquery generates a summary table of counts and ids, and then joins it to the other tables.
A JOIN cascade of this complexity may become inefficient for other reasons as your table grows if you don't structure your indexes correctly.