How Do I Use Case Statement Column In Group By

Question

As stated by the question, I\'m trying to formulate a query that has a case statement in the column results, and then I want to include that column in the query\'s group by stat

Answer 1

You can either use the case as is in the group by, like this:

SELECT SOME_TABLE_ALIAS.COLUMN1, OTHER_TABLE_ALIAS.COLUMN2,
CASE
    WHEN SOME_TABLE_ALIAS.COLUMN3 IS NOT NULL THEN 'A'
    ELSE 'B'
END AS CASE_COLUMN
FROM SOME_TABLE SOME_TABLE_ALIAS
... (other table joins and where clauses)
GROUP BY SOME_TABLE_ALIAS.COLUMN1, OTHER_TABLE_ALIAS.COLUMN2, 
CASE
    WHEN SOME_TABLE_ALIAS.COLUMN3 IS NOT NULL THEN 'A'
    ELSE 'B'
END

or use a sub-query like this:

select COLUMN1, COLUMN2, CASE_COLUMN
from (
    SELECT SOME_TABLE_ALIAS.COLUMN1, OTHER_TABLE_ALIAS.COLUMN2,
    CASE
        WHEN SOME_TABLE_ALIAS.COLUMN3 IS NOT NULL THEN 'A'
        ELSE 'B'
    END AS CASE_COLUMN
    FROM SOME_TABLE SOME_TABLE_ALIAS
    ... (other table joins and where clauses)
) a
GROUP BY COLUMN1, COLUMN2, CASE_COLUMN

Answer 2

The alias isn't available to use in the GROUP BY because when GROUP BY happens the alias isn't defined yet:

Here's the order:
1.FROM
2.WHERE
3.GROUP BY
4.HAVING
5.SELECT
6.ORDER BY

You can work around that with:

SELECT column1,column2,case_column
FROM (
SELECT SOME_TABLE_ALIAS.COLUMN1, OTHER_TABLE_ALIAS.COLUMN2,
CASE
    WHEN SOME_TABLE_ALIAS.COLUMN3 IS NOT NULL THEN 'A'
    ELSE 'B'
END AS CASE_COLUMN
FROM SOME_TABLE SOME_TABLE_ALIAS
... (other table joins and where clauses)
) a
GROUP BY COLUMN1, COLUMN2, CASE_COLUMN

Or just use the case you use in SELECT in GROUP BY