Question

我有这种mysql db（表名/字段）

tbl_users ：id，title，approved

tbl_photos ：id，user_id，title，filename

我在用户中有一行，有三张照片（所有用户都是user_id =用户的ID）

这样做：

select 
tbl_users.*, 
tbl_photos.filename 

from tbl_users 

left join tbl_photos on tbl_photos.user_id = tbl_users.id 

where tbl_users = '1' order by rand()

（表格查询简化了一点）

执行该sql查询返回三行。我只想要一行（即我想要用户行，以及任何具有该用户ID的user_id的随机照片）

我已经尝试了所有连接 - 左右内部但它们总是返回3行

Answer 1

您的代码应如下所示

select 
tbl_users.*, 
tbl_photos.filename 

from tbl_users 

left join tbl_photos on tbl_photos.user_id = tbl_users.id 

where tbl_users = approved order by rand() LIMIT 1

LIMIT关键字将限制查询仅返回1行。

可以在此处找到my-sql命令示例的简单列表 http://itswadesh.wordpress.com/2011/04/12/mysql-commands/

Answer 2

您还要添加DISTINCT：

select  DISTINCT tbl_users.id, 
        tbl_users.title, 
        tbl_users.approved, 
        tbl_photos.filename 
from tbl_users left join tbl_photos 
       on tbl_photos.user_id = tbl_users.id 
where tbl_users = 'approved' order by rand()

Answer 3

如果你想每个只有一行就这么做就很简单

select 
tbl_users.*, 
GROUP_CONCAT(tbl_photos.filename) as Photos

from tbl_users 

left join tbl_photos on tbl_photos.user_id = tbl_users.id 

where tbl_users = '1' order by rand()

它会在单个字段中为您提供逗号分隔值

Answer 4

如果文件名是您将从tbl_photos检索的唯一字段，则可以提供您所需的字段：

select 
    tbl_users.*, 

    (select filename 
     from tbl_photos where user_id = tbl_users.id 
     order by rand()
     limit 1) as filename

from tbl_users

如果您想要照片中的其他信息，这就是查询：

select tbl_users.*, 'x' as separator, tbl_photos.*
from tbl_users
left join tbl_photos on tbl_photos.user_id = tbl_users.id
where (tbl_users.id, tbl_photos.id) in

    (  
    -- you can run this query independently
        select 

            id, 

            (select id 
             from tbl_photos 
             where user_id = tbl_users.id 
             order by rand() 
             limit 1) 

        from tbl_users
    )

Mysql - 连接 - 返回的行数太多 - 每个连接表一个但不想要

4 个答案: