SQL error

[LKBrwn_DBA]

Try this:

SELECT DISTINCT
      CASE
          WHEN esc.x1 IN (SUBSTR (inp.y, 0, 3))
               AND esc.x2 IN (SUBSTR (inp.y, 4, 2), SUBSTR (inp.y, 4, 3))
           THEN
             esc.cc
          ELSE NULL
       END
  FROM xxx inp, yyy esc
 WHERE 
      CASE
          WHEN esc.x1 IN (SUBSTR (inp.y, 0, 3))
               AND esc.x2 IN (SUBSTR (inp.y, 4, 2), SUBSTR (inp.y, 4, 3))
           THEN
             esc.cc
          ELSE NULL
       END
          IS NOT NULL;