Question

我有一个名为messages的数据库表：

Column          Type    

global_ref_id   int(12)          
to              int(12)      
from            int(12)      
message         text             
status          int(1)   
viewed          int(1)

其中global_ref_id是消息的id（来自表事件的外键），是接收消息的用户的用户id，来自发送消息的用户的用户ID。

我想生成一个查询，该查询给出了显示每个用户向用户发送最后一条消息的结果（比如说其user_id为192），同时也将每个用户的消息总数提供给用户192.

直到现在我想出了这个查询来获得结果：

> SELECT messages.*
>                 FROM messages, events
>                 WHERE events.global_id = messages.global_ref_id
>                 AND to = 192
>                 GROUP BY messages.from
>                 ORDER BY events.event_time DESC

Answer 1

要更改查询的最小值，请执行以下操作（顺便未经测试）：

SELECT * FROM 
(
    SELECT messages.*,events.event_time, COUNT(messages.from) as "Total Messages Between Users"
    FROM messages, events
    WHERE events.global_id = messages.global_ref_id
    AND messages.to = 192
    GROUP BY messages.from
    ORDER BY messages.from
)
AS EVENTS
ORDER BY events.event_time
LIMIT 1;

LIMIT 1只会显示最后一条消息，如果您想要所有消息而不是最后一条消息，请删除。

Answer 2

结果显示每个用户向用户发送的最后一条消息（例如，其user_id为192）

SELECT 
    messages.message as 'Last Message'
FROM 
    messages, events
WHERE 
    events.global_id = messages.global_ref_id
AND to = 192
GROUP BY messages.from
ORDER BY events.event_time DESC
LIMIT 1

每个用户到用户192的消息总数

SELECT 
    messages.*, COUNT(messages.from) as "Total number of Messages to User"
FROM 
    messages, events
WHERE 
    events.global_id = messages.global_ref_id
AND to = 192
GROUP BY messages.from
ORDER BY events.event_time DESC

Answer 3

我认为这就是你想要的，但我只是MySQL新手。

http://sqlfiddle.com/#!2/d0586/8

m。to和m。from位于后面，因为它们是保留字。

希望它有所帮助！

Answer 4

SELECT
m.global_ref_id,
m.`to`,
m.`from`,
m.message,
m.status,
m.viewed
FROM messages m
WHERE m.global_ref_id = (SELECT max(i.global_ref_id)
                         FROM messages igroup
                         WHERE i.`to` = m.`to`
                         AND i.`from` = m.`from`);

会给你最新消息;获得总数将是另一个查询...

SELECT
m.`to`,
m.`from`,
count(*)
FROM messages m
GROUP BY m.`to`, m.`from`

合并这两个查询的输出是另一个问题！

Answer 5

最后我想出了答案，我不知道这个查询有多好，但它对我有用： -

SELECT messages.global_ref_id,
messages.`to`,
messages.`from`,
messages.message,
messages.status,
messages.viewed,
events.event_time,
count_table.msg_count as `total Number of messages`
FROM
messages
INNER JOIN
(select max(global_ref_id) as ref_id, count(*) msg_count from messages group by `from`)
as count_table
on (messages.global_ref_id = count_table.ref_id)
INNER JOIN events
on (events.global_id = messages.global_ref_id)
where messages.`to` = 192
order by events.global_id DESC

谢谢大家......

如何生成这个mysql查询

5 个答案: