test.sql

catme=> select
catme->   CASE
catme->     WHEN COALESCE(name, school) = '' THEN 'EMPTY STRING'
catme->     WHEN COALESCE(name, school) = NULL THEN 'NULL1'
catme->     WHEN COALESCE(name, school) IS NULL THEN 'NULL2'
catme->     ELSE COALESCE(name, school)
catme->   END as institution
catme-> from (
catme(>   SELECT 'name' as name, 'school' as school
catme(>   UNION ALL
catme(>   SELECT NULL as name, NULL as school
catme(>   UNION ALL
catme(>   SELECT '' as name, '' as school
catme(>   UNION ALL
catme(>   SELECT '1' as name, '' as school
catme(>   UNION ALL
catme(>   SELECT '2' as name, NULL as school
catme(>   UNION ALL
catme(>   SELECT '' as name, '3' as school
catme(>   UNION ALL
catme(>   SELECT NULL as name, '4' as school
catme(> ) as stuff(name, school);
 institution  
--------------
 name
 NULL2
 EMPTY STRING
 1
 2
 EMPTY STRING
 4
(7 rows)