Question

This is a summary version of the problems I am encountering, but hits the nub of my problem. The real problem involves huge UNION groups of monthly data tables, but the SQL would be huge and add nothing. So:

SELECT entity_id, 
    sum(day_call_time) as day_call_time
            from (
                SELECT entity_id, 
                    sum(answered_day_call_time) as day_call_time
                    FROM XCDRDNCSum201108 
                    where (day_of_the_month >= 10 AND  day_of_the_month<=24) 
                    and LPAD(core_range,4,"0")="0987" 
                    and LPAD(subrange,3,"0")="654" 
                    and SUBSTR(LPAD(core_number,7,"0"),4,7)="3210"
            ) as summary

is the problem: when the table in the subquery XCDRDNCSum201108 returns no rows, because it is a sum, the column values contain null. And entity_id is part of the primary key, and cannot be null.
If I take out the sum, and just query entity_id, the subquery contains no rows, and thus the outer query does not fail, but when I use sum, I get error 1048 Column ‘entity_id’ cannot be null

how do I work around this problem ? Sometimes there is no data.

Answer 1

You are completely overworking the query… pre-summing inside, then summing again outside. In addition, I understand you are not a DBA, but if you are ever doing an aggregation, you TYPICALLY need the criteria that its grouped by. In the case presented here, you are getting sum of calls for all entity IDs. So you must have a group by any non-aggregates. However, if all you care about is the Grand total WITHOUT respect to the entity_ID, then you could skip the group by, but would also NOT include the actual entity ID…

If you want inclusive to show actual time per specific entity ID…

SELECT
      entity_id, 
      sum(answered_day_call_time) as day_call_time,
      count(*) number_of_calls
   FROM
      XCDRDNCSum201108 
   where
          (day_of_the_month >= 10 AND  day_of_the_month<=24) 
      and LPAD(core_range,4,"0")="0987" 
      and LPAD(subrange,3,"0")="654" 
      and SUBSTR(LPAD(core_number,7,"0"),4,7)="3210"
   group by
      entity_id

This would result in something like (fictitious data)

Entity_ID   Day_Call_Time   Number_Of_Calls
1           10              3
2           45              4
3           27              2

If all you cared about were the total call times

SELECT
      sum(answered_day_call_time) as day_call_time,
      count(*) number_of_calls
   FROM
      XCDRDNCSum201108 
   where
          (day_of_the_month >= 10 AND  day_of_the_month<=24) 
      and LPAD(core_range,4,"0")="0987" 
      and LPAD(subrange,3,"0")="654" 
      and SUBSTR(LPAD(core_number,7,"0"),4,7)="3210"

This would result in something like (fictitious data)

Day_Call_Time   Number_Of_Calls
82              9