Question

我很想知道:

select * 
from Table1 T1 
left join Table1 T2 on T1.id = T2.id + 1 and (T2.id > 3)

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select * 
from Table1 T1 
left join Table1 T2 on T1.id = T2.id + 1 
where (T2.id > 3)

Answer 1

差异很大。

select * from Table1 T1 left join  Table1 T2 on T1.id=T2.id+1     where    (T2>3

条款在哪些地方将左边改为内 join,因为该条款不允许从左边返回无效价值。这意味着将排除左边会合谋记录的所有各行,因为退款的无效价值与3,并丢弃了行(这与使其成为内心结合具有同等效力)

第一份说明将过滤器纳入:

select * from Table1 T1 left join  Table1 T2 on T1.id=T2.id+1     and     (T2>3)

This means it will take effect and filter the rows that can be joined to using the left join, but this will not cause rows to be discarded when the left join fails to find a matching row.

Answer 2

In an INNER JOIN it doesn t matter where yuo put the condition.
It only makes a difference in a LEFT JOIN or RIGHT JOIN.

一段时间前,我就类似问题作了详细回答,解释了服务器在你两个案件中的每一个案件中都有所不同。

You can check it out here:
What is the difference in these two queries as getting two different result set?

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