Question

我有2张桌子，一个叫A，另一个叫B A与B具有相同的字段

我想做类似的事情

everything In A
and
distinct everything In
A join B on 
A.CustomerAccount = B.CustomerAccount
Or A.Email = B.Email
Or (A.CustomerAccount = B.CustomerAccount and A.Email = B.Email)

只是一个简短的说明，还有其他方法吗？（有更有效的方法吗？）

Answer 1

是的，在这种情况下，最好的解决方案是尝试使用UNION运算符并查看UNION examples。

基本句法-您的查询将代替OR：

SELECT * 
FROM (
    SELECT tpl.*, a.MidParentAId as 'MidParentId', 1 as 'IsMidParentA' 
    FROM TopLevelParent tpl 
    INNER JOIN MidParentA  a ON a.TopLevelParentId = tpl.TopLevelParentID
UNION
    SELECT tpl.*, b.MidParentBId as 'MidParentId', 0 as 'IsMidParentA'  
    FROM TopLevelParent tpl 
    INNER JOIN MidParentB b ON b.TopLevelParentId = tpl.TopLevelParentID
UNION
    SELECT tpl.*, 0 as 'MidParentId', 0 as 'IsMidParentA'  
    FROM TopLevelParent tpl 
    WHERE tpl.TopLevelParentID NOT IN (
       SELECT pa.TopLevelParentID 
       FROM TopLevelParent tpl
       INNER JOIN MidParentA  a ON a.TopLevelParentId = tpl.TopLevelParentID
    UNION
       SELECT pa.TopLevelParentID 
       FROM TopLevelParent tpl
       INNER JOIN MidParentB b ON h.TopLevelParentId = tpl.TopLevelParentID
    )
) tpl

Answer 2

您似乎想要：

select a.*
from a
union all
select distinct b.*
from b
where exists (select 1
              from a
              where b.CustomerAccount = a.CustomerAccount or
                    b.Email = a.Email
             );

我删除了条件：

(b.CustomerAccount = a.CustomerAccount and b.Email = a.Email)

因为它是多余的。

在多个OR条件下联接表

2 个答案: