对比
select * from A t1 left join B t2 on ( t1.c1 = t2.c1 or t1.c1=t2.c2)
select * from A t1 left join B t2 on
t1.c1 = t2.c1
left join B t3 on
t1.c1 = t3.c2
下面的比上面的快了几十倍
Original: https://www.cnblogs.com/cheng9999/p/15918656.html
Author: cheng_blog
Title: sql 优化
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