Zkuste toto:
SELECT DISTINCT loc
FROM [YourTable]
WHERE INSTR(CONCAT(', ',cat,' ,'),CONCAT(', ','$_POST[cat]',' ,'))>0 AND loc IS NOT NULL
Zkuste toto:
SELECT DISTINCT loc
FROM [YourTable]
WHERE INSTR(CONCAT(', ',cat,' ,'),CONCAT(', ','$_POST[cat]',' ,'))>0 AND loc IS NOT NULL