sql is the column value is null get column from another table : I have two tables. 
If percentage in table A is null then I want to look for it in table B

SELECT t.id,
CASE 
			WHEN t.percentage IS NULL
			THEN (SELECT percentage FROM test2 AS s WHERE s.id=t.id )
			ELSE t.percentage
	   END AS percentage
FROM [project_percentage] t
