[英]How to tell which query is the data fetched from in a MySQL statement with UNION
[英]MySQL key name of data array fetched with UNION
表objects
id name is_animal
-----------------------
1 dog 1
2 cat 1
3 chair 0
4 rabbit 1
查询
(SELECT name AS animal_name FROM objects WHERE is_animal = 1)
UNION
(SELECT name AS object_name FROM objects WHERE is_animal = 0)
和结果
[animal_name] => dog
[animal_name] => cat
[animal_name] => rabbit
[animal_name] => chair // expected: [object_name] => chair
我已经在第二个SELECT中使用了AS
,为什么它返回animal_name
而不是object_name
?
与UNION
:
(SELECT name AS animal_name,'' object_name FROM objects WHERE is_animal = 1)
UNION
(SELECT '' as animal_name, name AS object_name FROM objects WHERE is_animal = 0)
有case
:
select case is_animal when 1 name else '' end as animal_name,
case is_animal when 0 name else '' end as object_name
from objects
在UNION查询中,始终将第一个SELECT的列名选择为最终结果视图的列名。 如果每个单独的SELECT的对应列名称不同,您如何期望列名称结尾? 最好甚至不要在UNION查询的后续SELECT中提及列名,因为它没有任何意义。
从文档中 MySQL使用相同的
(SELECT 1 AS sort_col, col1a, col1b, ... FROM t1)
UNION
(SELECT 2, col2a, col2b, ... FROM t2) ORDER BY sort_col, col1a;
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