如何在SQL Server中的“select”语句中获取表名

我或多或少得做出这样的联合声明：

select [table_name], name, address
from Employees
where [my_condition]

UNION

select [table_name], name, address
from Employees_history
where [my_condition]

检索到的数据将在Employees或Employees_历史记录中，但不在这两个表中

我需要知道数据来自哪个表

SELECT 'Employees' AS [table_name],
       name,
       address
FROM   Employees
WHERE  [my_condition]
UNION ALL
SELECT 'Employees_history' AS [table_name],
       name,
       address
FROM   Employees_history
WHERE  [my_condition] 

我使用UNIONALL而不是UNION，因为两个分支之间不会有重复项。因此，它可以避免在整个结果集中删除重复项的一些不必要的工作

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如果分支中可能存在重复项，请向单个选项添加DISTINCT，您可以添加一个新字段，如下所示：

select [table_name], name, address, 'Employees'
from Employees
where [my_condition]

UNION

select [table_name], name, address, 'History'
from Employees_history
where [my_condition]

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您也可以使用一个别名，正如Martin在回答中所示

您不能执行以下操作：

select 'Employees' as table_name, name, address
from Employees
where [my_condition]

UNION

select 'Employees_history' as table_name, name, address
from Employees_history
where [my_condition]

这是可以实现的

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您的答案实际上没有使用任何表别名。

SELECT 'Employees' AS [table_name],
       name,
       address
FROM   Employees
WHERE  [my_condition]

UNION

SELECT 'History' AS [table_name],
       name,
       address
FROM   Employees_history
WHERE  [my_condition]