从多个表中选择数据? [英] SELECT Data from multiple tables?

问题描述

我有3个表，所有3个字段都相同.我基本上想从每个表中选择信息

I have 3 tables, with 3 fields all the same. I basically want to select information from each table

例如:

userid = 1

我想从所有3个表中选择数据，其中userid = 1

I want to select data from all 3 tables, where userid = 1

我当前正在使用:

   SELECT r.*, 
          p.*, 
          l.*
     FROM random r
LEFT JOIN pandom p ON r.userid = p.userid
LEFT JOIN landom l ON l.userid = r.userid
    WHERE r.userid = '1'
    LIMIT 0, 30

但这似乎不起作用.

推荐答案

具有3个相同的字段

with 3 fields all the same

所以您是说要从所有3个表中都the same 3 fields吗?

So you mean that you want the same 3 fields from all 3 tables?

   SELECT r.col1, r.col2, r.col3
     FROM random r
    WHERE r.userid = '1'
    LIMIT 0, 30
UNION ALL 
   SELECT p.pcol1, p.pcol_2, p.p3
     FROM pandom p
    WHERE p.userid = '1'
    LIMIT 0, 30
UNION ALL 
   SELECT l.l1, l.l2, l.l3
     FROM landom l
    WHERE l.userid = '1'
    LIMIT 0, 30

字段的名称不必相同，但相同的类型需要在位置1、2和3处对齐.

The fields don't have to be named the same, but the same types need to line up in position 1, 2 and 3.

限制的工作方式是:

• 它将尝试从random获取30.
• 如果已经有30张，它甚至不会查看其他2张桌子
• 如果random中的数量少于30，它将尝试填充pandom中的30，直到最后landom

• it will attempt to get 30 from random.
• If it has 30 already, it won't even look at the other 2 tables
• if it has less than 30 from random, it will try to fill up to 30 from pandom and only finally landom

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