SQL数据库操作的一个简单但是我不知道的东东！

ELECT  正 = SUM(CASE WHEN Amount > 0 THEN Amount
                     ELSE 0
                END)
      , 负 = SUM(CASE WHEN Amount < 0 THEN Amount
                     ELSE 0
                END)
      , UserName
FROM    tbl_Finance
GROUP BY UserName

-- 如果只需要求负

SELECT  SUM(Amount) AS Amount
      , UserName
FROM    tbl_Finance
WHERE Amount < 0
GROUP BY UserName