Question

This works:

 SELECT (CASE
             WHEN x = 'value' THEN
              a.col1
             ELSE
              nvl(a.col1, a.col2)
           END)
      FROM table1 a
     WHERE a.this = 'that'
     GROUP BY (CASE
                WHEN x = 'value'  THEN
                 a.col1
                ELSE
                 nvl(a.col1, a.col2)
              END)

But trying to have the case statement do an IN statement(trying for a more dynamic sql here), the following code results to an ORA-00979 error.

SELECT (CASE
         WHEN x IN (SELECT me FROM here WHERE this = 'example') THEN
          a.col1
         ELSE
          nvl(a.col1, a.col2)
       END)
  FROM table1 a
 WHERE a.this = 'that'
 GROUP BY (CASE
            WHEN x IN (SELECT me FROM here WHERE this = 'example') THEN
             a.col1
            ELSE
             nvl(a.col1, a.col2)
          END)

Is it possible to make this work or have an alternative? Thanks.
–Jonas

Benoit: Here’s a modified sql based on your sql that recreates the error:

select (case when a.y IN (select 'A'||ROWNUM from dual where rownum=1) then 1 else 0 end)
from (SELECT 'A'||ROWNUM y, 'B' x FROM DUAL CONNECT BY ROWNUM <= 3) a where x = 'B'
group by (case when a.y IN (select 'A'||ROWNUM from dual where rownum=1) then 1 else 0 end)
;

Basically what was missing was that the FROM table should have more than one values and that a column was referenced in the CASE statement.

Answer 1

I cannot reproduce this error with following request (working):

select (case when 'X' IN (select dummy from dual where rownum=1) then 1 else 0 end)
from dual
where dummy = 'X'
group by (case when 'X' IN (select dummy from dual where rownum=1) then 1 else 0 end)
;

Try:

WITH table1_extended AS (
   SELECT a.*, CASE WHEN x IN .... END "condition"
     FROM table1 a
)
SELECT b."condition"
  FROM table1_extended b
 WHERE b.this = 'that'
 GROUP BY b."condition"