Question

有两个表：

Clients
___________
idClient int
login varchar

Messages
___________
idMessage int
dateWakeup datetime
.... other fields

我需要每个客户端计算给定时间范围内表格中的条目数。我试过这样的事情：

SELECT c.login, count(m.idMessage) FROM Clients c, Messages m
where
    m.idClient=c.idClient and m.dateWakeup>'2010-09-01 00:00:01'
    and m.dateWakeup<'2010-10-01 00:00:01';

它不起作用。

Answer 1

使用COUNT(...)时，您必须GROUP BY您的结果：

SELECT c.login, count(m.idMessage)
FROM Clients c, Messages m
where m.idClient=c.idClient
and m.dateWakeup>'2010-09-01 00:00:01'
and m.dateWakeup<'2010-10-01 00:00:01'
GROUP BY c.login

Answer 2

试试这个

SELECT c.login, count(m.idMessage) FROM Clients as c
INNER JOIN Messages as m
ON m.idClient=c.idClient
WHERE m.dateWakeup BETWEEN '2010-09-01 00:00:01' and '2010-10-01 00:00:01'

Answer 3

SELECT c.login, count(m.idMessage) FROM Clients c, Messages m  
where m.idClient=c.idClient and m.dateWakeup>'2010-09-01 00:00:01' and
m.dateWakeup<'2010-10-01 00:00:01' GROUP BY c.login;

COUNT（）等聚合函数需要GROUP ... BY

如何加入我的“客户”和“消息”表？

3 个答案: