Question

I am not able to understand the SQL query output :

SQL> select distinct(STATUS) from TMP_ORDER_ACTION_PSTN_CP_11035;

    InDelivery_SOMBe 
    In Delivery
    Complete
    Amended
    Cancelled
    Failed InComplete
 1   SQL> select count(*) from TMP_ORDER_ACTION_PSTN_CP_11035 where
    STATUS='Complete';
          1484
 2   SQL>  select count(*) from TMP_ORDER_ACTION_PSTN_CP_11035 where STATUS
    != 'Complete';
          3167
  3  SQL> select count(*) from TMP_ORDER_ACTION_PSTN_CP_11035;
          5091

The sum of count for the 1 and 2 queries should be same as the total count(3 query).Why is the sum differing from the whole count?
It seems like a dump question but i dont know why is this happening.
Please note that My question is not related to null check at all.It is the that
sum(1+2)=3.1484+3167 !=5091.Why is the result different?

Answer 1

My guess is NULL values, which match none of your WHERE clauses, including the last one. Try

select count(*) from TMP_ORDER_ACTION_PSTN_CP_11035 where STATUS is null;

where status = null is never true, nor is where null = null. You have to use is null.

The sum of count for the 1 and 2 queries should be same as the total count(3 query).Why is the sum differing from the whole count?

No, because the records with NULL are not matching query 1 or query 2, but they are counted in query 3.

1 + 2 + IS NULL should equal 3.