Mysql：如何在UNION中添加虛擬列

Question

我想爲我的語句的第一個聯合的所有結果和下一個聯合的'enabled' = 0添加虛擬列'enabled' = 1。這是我迄今爲止的聲明...

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

只要指定新的列作爲源：

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

只是注意，你必須使用相同的列數具有相同數據使用union時的類型。