Question

我正在使用MySQL 5.5，我有以下sql：

UPDATE t SET val = 1  WHERE id IN ( SELECT id FROM temp1);
UPDATE t SET val = 2  WHERE id IN ( SELECT id FROM temp2 );
UPDATE t SET val = 3  WHERE id IN ( SELECT id FROM temp3 );
UPDATE t SET val = 4  WHERE id IN ( SELECT id FROM temp4 );
UPDATE t SET val = 5  WHERE id IN ( SELECT id FROM temp5 );
UPDATE t SET val = 6  WHERE id IN ( SELECT id FROM temp6 );
UPDATE t SET val = 7  WHERE id IN ( SELECT id FROM temp7 );
UPDATE t SET val = 8  WHERE id IN ( SELECT id FROM temp8 );
UPDATE t SET val = 9  WHERE id IN ( SELECT id FROM temp9 );
UPDATE t SET val = 10 WHERE id IN ( SELECT id FROM temp10 );

temps是我使用的TEMPORARY表，该表有大约10k个条目，完成此sql语句的执行大约需要30秒。临时表中所有条目的总和也等于t中的条目数。

我可以就如何优化这个提出一些建议吗？

感谢。

Answer 1

首先检查id列的“t”是否有索引（主键是最佳索引）

然后尝试使用以下内容对您的变体进行基准测试：

1

update t, (
select 1 as v, id from temp1
union all
select 2, id from temp2
...
) as q set val=q.v where t.id=q.id

2

truncate table t; -- note deletion of all from table t
insert into t (id, val)
select id, val from temp1
union all
select id, val from temp2
...

任何优化此查询的建议

1 个答案: