居住的縣市有幾個

/*目前員工所居住的縣市有幾個？*/


SELECT DISTINCT SUBSTRING(A.地址,1,3) AS 縣市
FROM 員工 AS A 

WITH 
TT
AS(
		SELECT DISTINCT SUBSTRING(A.地址,1,3) AS 縣市
		FROM 員工 AS A 
)
   SELECT COUNT(TT.縣市) FROM TT