将左外部联接转换为where语句

Question

I am looking to simplify this confusing left outer join statement into something easier to read by possibly using a where-statement

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

To something like:

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

This should do:

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

It looks like the join is trying to get orders that have at least one approved line but no unapproved lines. That should equate to

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 should work pretty fast for your usecase, and remove the need for both joins and inner queries:

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