Mysql:如何在UNION之前添加一个虚拟列

Question

我想为我语句的第一个并集的所有结果添加一个虚拟列 'enabled' = 1，为下一个联盟。这是我到目前为止的声明......

SELECT p.*
FROM member_permissions mp
JOIN permissions p ON p.permission_id = mp.permission_id
WHERE member_id = 1
UNION
SELECT pgp
FROM member_permissions mp
JOIN permission_link pl ON pl.permission_group_id = mp.permission_group_id
JOIN permissions pgp ON pgp.permission_id = pl.permission_id
WHERE member_id = 1
UNION        // this will have enabled = 0 //    
SELECT *
FROM permissions        

Answer 1

只需将新列指定为源:

select column1, column2, ..., 1 as enabled
from ....
union
select column1, column2, ..., 0 as enabled
from ....

请注意，在使用 union 时，必须使用相同数量的列和相同的数据类型。