I wrote a sql query to retrieve data as follows:

SELECT (MAX (b.filledqty) - MAX (a.filledqty)) AS filledtoday   
FROM clientordermas a, 
     clientordermas b  
WHERE a.clordid = 'w9110126'    
  AND b.clordid = 'w9110126'    
  AND (SELECT max(a.price) 
       FROM clientordermas a 
       WHERE a.clordid = 'w9110126') < 1000;

There are three records in the table for the given clordid with price values 800, 900 1200.

So, what I need is to get the difference between 1200 and 900 which is 300.

But, the above statement always returns 0. What I should get is MAX (b.filledqty) retuns 1200 and MAX (a.filledqty) retuns 900.

But it is not happening. This is not the exact problem I am facing but a simplified version of it.

Can someone please help?