Question

我必须在join（SQL Server）中使用条件语句

select * from A inner join B
on A.id = B.id

如果B.id is null or B.id = ''它应该是A.id2 = B.id2而不是A.id = B.id

如果我做这样的事情是否正确：

   select * from A inner join B on  
   (B.id is not null and B.id <> '' and A.id = B.id) or 
   ((B.id is null or B.id = '') and A.id2 = B.id2)

Answer 1

我认为这不是解决这个问题的最佳方法，但可能很有用，也很简单：

SELECT * FROM a INNER JOIN b
 ON a.id = b.id
UNION 
SELECT * FROM a INNER JOIN b
 ON a.id2 = b.id2
 WHERE b.id IS NULL OR b.id = ''

Answer 2

select * from A inner join B
on (A.id = B.id) OR ((B.id is null or B.id = '') && (A.id2 = B.id2))

Answer 3

使用CASE声明

SELECT *
FROM A
INNER JOIN B
ON  CASE
        WHEN B.id IS NULL OR B.id = '' THEN A.id2
        ELSE A.id
    END
    =
    CASE
        WHEN B.id IS NULL OR B.id = '' THEN B.id2
        ELSE B.id
    END

Answer 4

试试这段代码

  DECLARE @b varchar(50)=(SELECT id FROM b)
DECLARE @a varchar(50)=(SELECT id FROM a)
if ((@b in (null , '')) and (@a in (null , '')))

BEGIN

select * from A inner join B
on
A.name = B.name 

END
else

BEGIN

select * from A inner join B
on A.id = B.id 

END

join语句中的SQL条件

4 个答案: