SQL Query optimization : Taking lots of time

Question

I am having the following query used to retrieve a set of orders:

select count(distinct po.orderid) 
from PostOrders po, 
     ProcessedOrders pro 
where pro.state IN ('PENDING','COMPLETED') 
  and po.comp_code in (3,4) 
  and pro.orderid = po.orderid

The query returns a result of 4323, and does so fast enough.

But I have to put another condition such that it returns only if it is not present in another table DiscarderOrders for which I add an extra condition to the query:

select count(distinct po.orderid) 
from PostOrders po, 
     ProcessedOrders pro 
where pro.state IN ('PENDING','COMPLETED') 
  and po.comp_code in (3,4) 
  and pro.orderid = po.orderid 
  and po.orderid not in (select do.order_id from DiscardedOrders do)

The above query takes a lot of time and just keeps on running. Is there anything I can do to the query such that it executes fast? Or do I need to execute the first query first, and then filter based on the condition by shooting another query?

Answer 1

You can try to replace:

and po.orderid not in (select do.order_id from DiscardedOrders do)

by

and not exists (select 1 from DiscardedOrders do where do.order_id = po.orderid)

Answer 2

try using JOIN than NOT IN

SELECT  COUNT(DISTINCT po.orderid) TotalCount
FROM    PostOrders po
        INNER JOIN ProcessedOrders pro
            ON po.orderid = pro.orderid
        LEFT JOIN DiscardedOrders do
            ON po.orderid = do.orderid
WHERE   po.comp_code IN (3,4) AND
        pro.state IN ('PENDING','COMPLETED') AND
        do.orderid IS NULL

OR NOT EXISTS

SELECT  COUNT(DISTINCT po.orderid) TotalCount
FROM    PostOrders po
        INNER JOIN ProcessedOrders pro
            ON po.orderid = pro.orderid
WHERE   po.comp_code IN (3,4) AND
        pro.state IN ('PENDING','COMPLETED') AND
        NOT EXISTS
        (
            SELECT  1
            FROM    DiscardedOrders do
            WHERE   po.orderid = do.orderid
        )

Answer 3

Same as distinct:

SELECT count(po.orderid) 
  FROM PostOrders po 
 WHERE po.comp_code IN (3,4) 
   AND EXISTS 
   (
   SELECT 1 FROM ProcessedOrders pro 
    WHERE pro.orderid = po.orderid
      AND pro.state IN ('PENDING','COMPLETED') 
   )
  ....
 /