从下面的代码示例中,为什么我需要在JOIN子句中使用括号(),例如在使用(Publisher_Code)的JOIN PUBLISHER中?
我知道不使用括号会返回错误,但我想知道机器本身是如何读取这条语句的。
SELECT
Book_Title as 'Title',
Publisher_Name
FROM BOOK
JOIN PUBLISHER USING (Publisher_Code)
JOIN WROTE USING (Book_Code)
JOIN AUTHOR USING (Author_Num)
group by Boo, k_Title, Publisher_Name
having count(distinct concat(LastName,FirstName)) = 2
谢谢!
发布于 2019-06-09 23:37:47
避免模棱两可。假设你这样做了:
from a join
b
using c, d
SQL不会知道您想要其中的哪一个:
from a join
b
using (c, d)
或者:
from a join
b
using c cross join
d
因此,该标准要求使用圆括号。
https://stackoverflow.com/questions/56515931
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