SQL在CASE中使用DISTINCT

Question

我有以下查询：

SELECT M.TYPE, COUNT(F.CD) AS TOTAL,
COUNT(CASE WHEN F.GENDER=0 THEN F.GENDER END) AS NUM_MALE,
COUNT(CASE WHEN F.GENDER=1 THEN F.GENDER END) AS NUM_FEMALE
FROM MARC M
LEFT JOIN FUNCION F ON M.CD_FUNCION = F.CD
GROUP BY 1  

即使FUNCION在表MARC中有多行，此查询也会按TYPE返回所有计数。但如果我只想要 DISTINCT FUNCIONS我该怎么办呢？第一次计算很简单，但我如何使用DISTINCT分隔男性和女性？

提前致谢！

Answer 1

您可以将COUNT DISTINCT与条件聚合一起使用：

SELECT M.TYPE, COUNT(DISTINCT F.CD) AS TOTAL,
       COUNT(DISTINCT CASE WHEN F.GENDER = 0 THEN F.CD END) AS NUM_MALE,
       COUNT(DISTINCT CASE WHEN F.GENDER = 1 THEN F.CD END) AS NUM_FEMALE
FROM MARC M LEFT JOIN
     FUNCION F
     ON M.CD_FUNCION = F.CD
GROUP BY M.TYPE;