Count distinct in case statement

Question

SELECT A.P_ID,
B.P_NAME,
C.P_DESC,
SUM(CASE
WHEN A.DATE BETWEEN TRUNC(ADD_MONTHS(LAST_DAY(SYSDATE),-4) + 1) AND ADD_MONTHS(LAST_DAY(TO_DATE(SYSDATE)),-1)
AND A.M_ID IS NOT NULL
THEN 1
ELSE 0
END) AS COUNT,
SUM(CASE
WHEN A.DATE BETWEEN TRUNC(ADD_MONTHS(LAST_DAY(SYSDATE),-4) + 1) AND ADD_MONTHS(LAST_DAY(TO_DATE(SYSDATE)),-1)
AND A.M_ID IS NOT NULL
THEN COUNT(DISTINCT A.M_ID)
ELSE 0
END) AS UNIQUE_COUNT, /* Not possible */
SUM(CASE
WHEN A.DATE BETWEEN TRUNC(SYSDATE,'YEAR') AND ADD_MONTHS(LAST_DAY(TO_DATE(SYSDATE)),-1)
THEN A.AMT_1
ELSE 0
END) AS TOTAL_AMT_1,
SUM(CASE
WHEN A.DATE BETWEEN TRUNC(SYSDATE,'YEAR') AND ADD_MONTHS(LAST_DAY(TO_DATE(SYSDATE)),-1)
THEN A.AMT_2
ELSE 0
END) AS TOTAL_AMT_2
FROM TABLE_A A,
TABLE_B B,
TABLE_C C
WHERE A.P_ID = B.P_ID
AND B.PT_ID = C.PT_ID
GROUP BY A.P_ID,
B.P_NAME,
C.P_DESC
Hi,
This is a simplified version of my query.
I am trying to do 4 things here,
1. count A.M_ID
2. count distinct A.M_ID, this is where I have a problem.
3. and 4. Its just the sum from 2 diff columns.
Note that the dates for count and amt are different and I can't hard code them.
Can any one help me in the distinct count step?
This query is also running kinda slow.
So any suggestions, comments are very welcome.
Note: TABLE_A has 700 million recs, TABLE_B 4 million and TABLE_c is just 500 recs
Thanks!

Answer 1

Taking advantage of the fact that most aggregate functions ignore nulls, you could do something like:
SELECT a.p_id, b.p_name, c.p_desc,
       COUNT(CASE WHEN a.date BETWEEN TRUNC(ADD_MONTHS(LAST_DAY(sysdate),-4) + 1) AND
                                      ADD_MONTHS(LAST_DAY(TO_DATE(sysdate)),-1) AND
                       a.m_id IS NOT NULL THEN m_id END) AS countall,
       COUNT(DISTINCT CASE WHEN a.date BETWEEN TRUNC(ADD_MONTHS(LAST_DAY(sysdate),-4) + 1) AND
                                    ADD_MONTHS(LAST_DAY(TO_DATE(sysdate)),-1) AND
                     a.m_id IS NOT NULL THEN a.m_id END) AS unique_count, /* entirely possible */
       SUM(CASE WHEN a.date BETWEEN TRUNC(sysdate,'YEAR') AND
                                    ADD_MONTHS(LAST_DAY(TO_DATE(sysdate)),-1) THEN a.amt_1
                ELSE 0 END) AS total_amt_1,
       SUM(CASE WHEN A.DATE BETWEEN TRUNC(sysdate,'YEAR') AND
                                    ADD_MONTHS(LAST_DAY(TO_DATE(sysdate)),-1) THEN A.AMT_2
                ELSE 0 END) AS TOTAL_AMT_2
FROM table_a a, table_b b, table_c c
WHERE a.p_id = b.p_id and
      b.pt_id = c.pt_id
GROUP BY a.p_id, b.p_name, c.p_descThe two case statements inside the COUNT return either a.m_id or NULL. A simplified test case is:
SQL> WITH t as (
  2     SELECT 1 m_id, 9 dt FROM dual UNION ALL
  3     SELECT 1 m_id, 6 dt FROM dual UNION ALL
  4     SELECT 2 m_id, 9 dt FROM dual UNION ALL
  5     SELECT 2 m_id, 6 dt FROM dual UNION ALL
  6     SELECT 1 m_id, 5 dt FROM dual UNION ALL
  7     SELECT 2 m_id, 5 dt FROM dual UNION ALL
  8     SELECT null m_id, 9 dt FROM dual)
  9  SELECT count(CASE WHEN dt BETWEEN 6 and 9 THEN m_id end) cid,
10         count(distinct CASE WHEN dt BETWEEN 6 and 9 THEN m_id end) cdid
11  FROM t;
       CID       CDID
         4          2I'm not entirely sure that you actually need the a.m_id IS NOT NULL predicate in the CASE statements, but I left it to be safe.
John