Question

我目前使用子查询工作，但随着数据库的增长，这将变得非常低效。我想知道是否有更有效的方法可以在没有子查询的情况下做我需要做的事情？

我需要让我的最终输出看起来像这样：

Question, Answer, Responses, Charts included in Response Count
Did this work?, N/A, 26, 30
Did this work?, Yes, 4, 30

这是我目前的查询：

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

完美无缺，问题是它必须使用子查询，随着时间的推移效率会降低。

我只是想知道在没有它的情况下是否有更好的方法来完成这个求和字段。

Answer 1

据推测，您关注的子查询是您的顶级SELECT中的子查询。

这很容易重构，所以不会重复。

只需将其加入表格的其余部分即可。你会想要这样的事情：

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

countup子查询生成计数和ID的汇总表，然后将其连接到其他表。

如果您没有正确构建索引，那么由于其他原因，这种复杂性的JOIN级联可能会变得低效。

MySQL - 没有子查询的多行和

1 个答案: