sql语句中Left join的on和where

Question

问题是并了几张表，其中有left join 或者inner join的，比如下面这样

SELECT * from 
(SELECT a.inserttime, a.Num 
FROM test.contract a 
LEFT JOIN test.customer b ON a.Num = b.Num2) tmp 
LEFT JOIN test.customer4 d ON tmp.num = d.num4 ; 

然后现在想取出的是a.inserttime > '2019-5-5'的数据，该用where还是on呢？
该写在哪里？是要在最外面再包一层select用where a.inserttime > '2019-5-5'吗？

Answer 1

以mysql为例，
查询条件insertime，直接写在括号里，由于有外联，where条件写在括号内的外联后，

SELECT * from 
(SELECT a.inserttime, a.Num 
FROM contract a 
LEFT JOIN customer b ON a.Num = b.Num2
WHERE a.inserttime > '2019-07-28') tmp 
LEFT JOIN customer4 d ON tmp.num = d.num4 ;