SUM function to give NULL result

Question

I am really lost on how I can force the SUM function to give me a NULL result when at least one of the elements is a NULL value. I would appreciate any help.

Answer 1

The short answer is "you can't". The slightly longer answer is the you can't because most aggregate functions work only on non-null values, so SUM silently ignores NULLS.
However, you can take advantage of that fact to do what you want.
SQL> SELECT * FROM t;
        ID GROUPCOL
        33 GROUPA
        50 GROUPA
         5 GROUPA
        21 GROUPA
        43 GROUPA
        58 GROUPB
        10 GROUPB
        29 GROUPB
        10 GROUPB
        37 GROUPB
           GROUPA
SQL> SELECT groupcol, SUM(id) sum_id, COUNT(*) count_all,
  2               COUNT(id) count_id
  3        FROM t
  4        GROUP BY groupcol;
GROUPCOL       SUM_ID  COUNT_ALL   COUNT_ID
GROUPA            152          6          5
GROUPB            144          5          5Note that count_all is different than count_id. So, we can wrap this query in another to return NULL for the sum of groupa.
SQL> SELECT groupcol, CASE WHEN count_all = count_id THEN sum_id
  2                        ELSE NULL END sum_id
  3  FROM (SELECT groupcol, SUM(id) sum_id, COUNT(*) count_all,
  4               COUNT(id) count_id
  5        FROM t
  6        GROUP BY groupcol);
GROUPCOL       SUM_ID
GROUPA
GROUPB            144Although, I too would be interested in the answer to 405764's question.
John