Question

我希望通过使用where-statement

将这种令人困惑的左外连接语句简化为易于阅读的内容

Select approved.orderId
From  (select distinct orderId from OrderLine where isApproved = 1 and isDismissed = 0) approved
      left outer join 
      (select distinct orderId from OrderLine where isApproved = 0 and isDismissed = 0) unapproved 
      on approved.orderId = unapproved.orderId
Where unapproved.orderId Is Null

类似于：

Select orderId
From  (select distinct orderId from OrderLine where (isApproved = 1 and isDismissed = 0) OR (isApproved = 0 and isDismissed = 0 and orderId is null))

Answer 1

这应该做：

SELECT DISTINCT O.orderId
FROM OrderLine O
WHERE O.isDismissed = 0
AND O.isApproved = 1
AND NOT EXISTS( SELECT 1 FROM OrderLine
                WHERE isApproved = 0
                AND isDismissed = 0
                AND orderId = O.OrderId)

Answer 2

看起来联接正在尝试获得至少有一条已批准的行但没有未批准的行的订单。这应该等同于

select distinct orderId 
from OrderLine
where isApproved = 1 
  and isDismissed = 0
  AND orderID NOT IN 
      (select orderId 
       from OrderLine 
       where isApproved = 0 
         and isDismissed = 0)

Answer 3

except应该可以很快地用于您的用例，并且不再需要连接和内部查询：

SELECT DISTINCT orderId
FROM   orderline
WHERE  isApproved = 1 and isDismissed = 0
EXCEPT
SELECT orderId
FROM   orderline
WHERE  isApproved = 0 and isDismissed = 0

将左外连接转换为where语句

3 个答案: