Question

I have a sql table with following values

       |  col1 | col2|   source |  values
       |  1    |  2  |  A       |   null
       |  1    |  2  |  B       |   1.0
       |  1    |  2  |  C       |   null
       |  1    |  4  |  A       |   2.0
       |  1    |  4  |  B       |   2.0
       |  1    |  4  |  C       |   2.0
       |  1    |  5  |  A       |   null
       |  1    |  5  |  B       |   null
       |  1    |  5  |  C       |   null

How can I get an output with a group by of col1 and col2 with a flag:

• all values match for a group ( flag = 1)
• all values are null ( flag = 2)
• some values is null (flag = 3)

Output:

       |  col1 | col2|   flag
       |  1    |  2  |   3
       |  1    |  4  |   1
       |  1    |  5  |   2

Answer 1

Or: based on your updated question:

  SELECT 
    col1, 
    col2,
    SUM(CASE WHEN SomeConditionHere THEN 1 ELSE 0 END) AS Flag
  FROM Table1
  GROUP BY col1, col2;

SQL Fiddle Demo

This will give you:

| COL1 | COL2 | FLAG |
----------------------
|    1 |    2 |    2 |
|    1 |    4 |    0 |
|    1 |    5 |    3 |

Note that: I assumed that the flag is how many NULL values are in the VALUES column, so I used "Values" IS NULL instead of SomeConditionHere.

I couldn’t understand how the flag should be computed in the expected results you posted. You have to use the predicate that define your flag instead of "Values" IS NULL.

Update:

Try this:

WITH Flags
AS
(
  SELECT 
    col1, col2,
    COUNT(*) ValuesCount,
    SUM(CASE WHEN "Values" IS NULL THEN 1 ELSE 0 END) AS NULLValues
  FROM Table1 
  GROUP BY col1, col2
)
SELECT 
  col1,
  col2,
  Flag = CASE WHEN ValuesCount = NULLValues THEN 2
              WHEN NULLVALUES = 0 
               AND ValuesCount = (SELECT COUNT(*) 
                                  FROM Table1 t2
                                  WHERE t1.col1 = t2.col1
                                    AND t1.col2 = t2.col2) THEN 1
               ELSE 3
END
FROM Flags t1;

Updated SQL Fiddle Demo

This will give you:

| COL1 | COL2 | FLAG |
----------------------
|    1 |    2 |    3 |
|    1 |    4 |    1 |
|    1 |    5 |    2 |