Question

这是mysql上的“msg”表

sent_to  customer   msg      read
-------  --------  ------   -----
45          3       bla       0
34          4        bla       1
34          6        bla       0
45          3        bla       0
56          7        bla       1
45          8        bla       0

例如id为45登录的用户，

我希望他看到这个，

you have 2 unread msg to your "number 3" customer
you have 1 unread msg to your "number 8" customer

就像新闻提要

我应该使用什么查询？

THX

Answer 1

您可能需要使用以下查询。

SELECT   CONCAT('You have ', 
                COUNT(`read`), 
                ' unread msg to your number ', 
                customer, 
                ' customer') AS news
FROM     msg 
WHERE    `read` = '0' AND `sent_to` = '45'
GROUP BY customer;

请注意，read是MySQL中的保留字，因此您必须将其括在反引号中。（Source）

测试用例：

CREATE TABLE msg (
    `sent_to`    int,
    `customer`   int,
    `msg`        varchar(10),
    `read`       int
);

INSERT INTO msg VALUES(45, 3, 'bla', 0);
INSERT INTO msg VALUES(34, 4, 'bla', 1);
INSERT INTO msg VALUES(34, 6, 'bla', 0);
INSERT INTO msg VALUES(45, 3, 'bla', 0);
INSERT INTO msg VALUES(56, 7, 'bla', 1);
INSERT INTO msg VALUES(45, 8, 'bla', 0);

查询结果：

+-------------------------------------------------+
| news                                            |
+-------------------------------------------------+
| You have 2 unread msg to your number 3 customer |
| You have 1 unread msg to your number 8 customer |
+-------------------------------------------------+
2 rows in set (0.00 sec)

Answer 2

SELECT COUNT(read), customer FROM msg WHERE read = 0 AND sent_to = '45' GROUP BY customer;

Answer 3

select count(sent_to), customer
from msg 
where read < 1
and sent_to = 45
group by customer

Answer 4

...

select count(*), customer from msg where read = 0 group by customer

简单的mysql查询问题

4 个答案: