SQL case statement not executing 'else'
You used this predicate: COLUMN_A = 'NA'

The result of COUNT(COLUMN_A) can be 0 only if you have 0 rows where COLUMN_A = 'NA' (as nulls are excluded because of the predicate). If you have 0 rows, the CASE statement is not evaluated at all, and the above query returns no result.

You need a query that returns result even if no rows match your predicate. E.g:

SELECT 
  CASE
    WHEN C = 1
      THEN 'PASS'
    WHEN C &gt; 1
      THEN 'FAIL'
    ELSE 'DOES NOT EXIST',
    'NA'
FROM
(
  SELECT COUNT(*) AS C
  FROM SCHEMA.TABLE_A SCH
  WHERE SCH.COLUMN_A = 'NA'
);