MySQL

Question

我有一个带有 100 个 *_options table 的 WordPress 多站点，即 WPM_101_options 到 WPM_201_options。

我正在尝试查询选项名称 admin_email、siteurl 和 blogname。

此代码适用于 1 table:

SELECT option_name, option_value 
FROM wpm_104_options
WHERE option_name = 'admin_email' 
UNION
SELECT option_name, option_value 
FROM wpm_104_options
WHERE option_name = 'siteurl'
UNION
SELECT option_name, option_value 
FROM wpm_104_options
WHERE option_name = 'blogname'

但是如何让它与多个 table 一起工作？我尝试了 2 tables...

SELECT option_name, option_value 
FROM wpm_104_options,wpm_105_options
WHERE option_name = 'admin_email' 
UNION
SELECT option_name, option_value 
FROM wpm_104_options,wpm_105_options
WHERE option_name = 'siteurl'
UNION
SELECT option_name, option_value 
FROM wpm_104_options,wpm_105_options
WHERE option_name = 'blogname'

和

SELECT option_name, option_value 
FROM wpm_104_options,wpm_101_options
WHERE option_name = 'admin_email' 
GROUP BY option_name
UNION
SELECT option_name, option_value 
FROM wpm_104_options,wpm_101_options
WHERE option_name = 'siteurl'
GROUP BY option_name
UNION
SELECT option_name, option_value 
FROM wpm_104_options,wpm_101_options
WHERE option_name = 'blogname'
GROUP BY option_name

和

SELECT wpm_104_options.option_name as n104, wpm_104_options.option_value as v104, wpm_101_options.option_name as n101, wpm_101_options.option_value as v101
FROM wpm_104_options, wpm_101_options
WHERE option_name = 'admin_email'

...但是我得到一个错误：

Error Code: 1052. Column 'option_name' in field list is ambiguous 0.000 sec

Answer 1

错误表明您已尝试查询两个 table，每个都有一个 option_name 列，而数据库无法知道您指的是哪两个。

您在 FROM 子句中指定两个 table 所做的是一个 implicit join。如果您希望将两个 table 中的列加入您的结果中，您需要通过在它们前面加上 table 名称来指定您所指的列，例如

SELECT wpm_104_options.option_name, wpm_104_options.option_value, wpm_101_options.option_name, wpm_101_options.option_value 
FROM wpm_104_options,wpm_101_options
WHERE wpm_104_options.option_name = 'admin_email' 
GROUP BY wpm_104_options.option_name

然而，这通常只有在您还指定列应该以何种方式连接时才有意义，即在 WHERE 子句中定义它们的关系。否则，您只会从两个 table 中获得所有可能的行组合。

我猜你真正想要的是别的东西。我相信您只是想要显示一个 table 和两个 table 的查询的组合结果。这不是通过在 FROM 子句中使用两个 table 的隐式连接来实现的，而是像您已经使用的那样使用 UNION 或 UNION ALL。例如

SELECT option_name, option_value 
FROM wpm_104_options
WHERE option_name = 'admin_email' 
UNION
SELECT option_name, option_value 
FROM wpm_104_options
WHERE option_name = 'siteurl'
UNION
SELECT option_name, option_value 
FROM wpm_104_options
WHERE option_name = 'blogname'
UNION 
SELECT option_name, option_value 
FROM wpm_101_options
WHERE option_name = 'admin_email' 
UNION
SELECT option_name, option_value 
FROM wpm_101_options
WHERE option_name = 'siteurl'
UNION
SELECT option_name, option_value 
FROM wpm_101_options
WHERE option_name = 'blogname'

您还可以通过在 WHERE 子句中使用 OR:

指定不同的条件来大大缩短这个时间

SELECT option_name, option_value 
FROM wpm_104_options
WHERE option_name = 'admin_email' 
   OR option_name = 'siteurl'
   OR option_name = 'blogname'
UNION 
SELECT option_name, option_value 
FROM wpm_101_options
WHERE option_name = 'admin_email' 
   OR option_name = 'siteurl'
   OR option_name = 'blogname'

甚至

SELECT option_name, option_value 
FROM wpm_104_options
WHERE option_name IN ('admin_email', 'siteurl', 'blogname')
UNION 
SELECT option_name, option_value 
FROM wpm_101_options
WHERE option_name IN ('admin_email', 'siteurl', 'blogname')

MySQL - Select 来自多个表并显示多个字段

MySQL - Select from multiple tables and display multiple fields

sql

union

select

join