select A.key
from A left join C on A.XX = C.key
left join B on C.YY = B.key
select A.key
from A left join (select C.key
from C left join B on C.YY = B.key) D
on A.XX = D.key大大们帮忙看一下上面两中写法效果一样么
from A left join C on A.XX = C.key
left join B on C.YY = B.key
select A.key
from A left join (select C.key
from C left join B on C.YY = B.key) D
on A.XX = D.key大大们帮忙看一下上面两中写法效果一样么
解决方案 »
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