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MySQL 相关项目 MariaDB Drizzle 参考文档 http://mysql-python.sourceforge.net/MySQLdb.html
MySQL 相关项目 MariaDB Drizzle 参考文档 http://mysql-python.sourceforge.net/MySQLdb.html 
这是一个创建于 99 天前的主题，其中的信息可能已经有所发展或是发生改变。
最近在 mysql 中做了一个查询
select count(*) from
(select a,b,count(distinct c) from table group by a,b having count(distinct c)>=2) as t
把 mysql 库跑死掉了
请教下有什么可以优化的空间？
目前想到的是下面
select count(*) from
(select a,b from table group by a,b having count(distinct c)>=2) as t
select count(*) from
(select a,b,count(distinct c) from table group by a,b having count(distinct c)>=2) as t
把 mysql 库跑死掉了
请教下有什么可以优化的空间？
目前想到的是下面
select count(*) from
(select a,b from table group by a,b having count(distinct c)>=2) as t
 | 1 supersf OP Gemini 反馈可以用 min 和 max SELECT count(*) FROM ( SELECT a, b FROM table GROUP BY a, b HAVING min(c) <> max(c) ) AS t; |
2 lyis 99 天前 1.加索引 (a,b,c) 2.试试 SELECT a,b FROM table T1 WHERE EIXSTS( SELECT 1 FRO table T2 WHERE T1.a=T2.a and T1.b=T2.b and T1.c<>T2.c ) |
 | 3 andykuen959595 99 天前 数据有多少？按 2 楼的方法，给 abc 加个索引试试 |
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