2
SELECT SUM(mark) AS totalMark, userID, credit
FROM users, marks
WHERE marks.receiverID = users.userID
AND userID = '2'
它将返回
totalMark userID credit
---------------------------
0 2 0.0
而这是非常好的,没问题。但这里的情况是2:
SELECT SUM(mark) AS totalMark, userID, credit
FROM users, marks
WHERE marks.receiverID = users.userID
AND userID = '-1'
结果:
totalMark userID credit
---------------------------
NULL NULL NULL
但我要的是什么也不返回(找不到记录)。任何人都可以帮助我?
任何时候,你会得到至少一排。 – Kermit 2013-03-07 18:32:45