sql - 是否可以在sql查询期间设置标志

Question

我正在尝试执行这样的 SQL 查询

(SELECT ID, Name FROM Book)
UNION
(SELECT ID, Name FROM Author)

我想在决赛桌中知道哪些 id 来自书本，哪些来自作者设置标志或类似的东西。

Answer 1

你可以这样做：

SELECT ID, Name, 'From Book' AS FromWhome 
FROM Book
UNION
SELECT ID, Name, 'From Author'
FROM Author

Answer 2

只需选择一个静态文本，例如

(SELECT ID, Name, "Book" FROM Book) UNION (SELECT ID, Name, "Author" FROM Author)

Answer 3

选择值允许列和表达式，您也可以用这种方式命名新列结果：

SELECT ID, Name, 'book' as tag FROM Book
UNION 
SELECT ID, Name, 'author' as tag FROM Author