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我有一个很长的查询正在占用资源并且需要重写它。它的明显问题是在 where 子句中使用了“not in”。我最初的想法是重写它，取消所有自连接并在子查询上执行“不存在”。关于这样做的任何想法，或者比那个更有效的想法？

这是查询：

SELECT a.referenceid,
       a.memberid AS d1,
       b.memberid AS d2,
       c.memberid AS d3,
       d.memberid AS d4,
       e.memberid AS d5,
       f.memberid AS d6
FROM   jos_comprofiler_members AS a FORCE INDEX (aprm)
       LEFT JOIN jos_comprofiler_members AS b FORCE INDEX (aprm)
              ON a.memberid = b.referenceid
                 AND b.accepted = 1
                 AND b.pending = 0
       LEFT JOIN jos_comprofiler_members AS c FORCE INDEX (aprm)
              ON b.memberid = c.referenceid
                 AND c.accepted = 1
                 AND c.pending = 0
       LEFT JOIN jos_comprofiler_members AS d FORCE INDEX (pamr)
              ON c.memberid = d.referenceid
                 AND d.accepted = 1
                 AND d.pending = 0
       LEFT JOIN jos_comprofiler_members AS e FORCE INDEX (pamr)
              ON d.memberid = e.referenceid
                 AND e.accepted = 1
                 AND e.pending = 0
       LEFT JOIN jos_comprofiler_members AS f FORCE INDEX (pamr)
              ON e.memberid = f.referenceid
                 AND f.accepted = 1
                 AND f.pending = 0
WHERE  a.referenceid = 1593
       AND a.accepted = 1
       AND a.pending = 0
       AND f.memberid = 1593
       AND b.memberid NOT IN ( 1593, a.memberid )
       AND c.memberid NOT IN ( 1593, a.memberid, b.memberid )
       AND d.memberid NOT IN ( 1593, a.memberid, b.memberid, c.memberid )
       AND e.memberid NOT IN (
           1593, a.memberid, b.memberid, c.memberid, d.memberid )
       AND f.memberid NOT IN ( 1593, a.memberid, b.memberid, c.memberid,
                               d.memberid, e.memberid )
LIMIT  0, 1
4

1 回答 1

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您的查询正在寻找 1593 距离 6 内的所有成员。反问：这与六度分离有关吗？

通常，在 SQL 中查找此类列表需要递归查询或一些非 SELECT 构造（循环、游标）。not in当列表由变量成员组成时，我不确定 MySQL 如何处理. 但是，我怀疑它正在为每个循环连接做某种嵌套循环连接。

建议：将not in语句移到on子句中。例如：

   LEFT JOIN jos_comprofiler_members AS c FORCE INDEX (aprm)
          ON b.memberid = c.referenceid
             AND c.accepted = 1
             AND c.pending = 0
             AND (c.memberId <> b.MemberId an c.MemberId <> a.MemberId and c.MemberId <> 1593)

这可以改善事情。或者让他们变得更糟。但这是一个想法。

于 2012-12-05T20:23:57.110 回答