mysql - SQL查询根据条件返回额外的列

Question

我想做一个查询，它将根据满足什么条件添加一列(我尝试使用 sequelize 没有获得我想要的结果)因此我想尝试使用纯 SQL，因为它没有那么多限制。
例子:SELECT * FROM db.messages WHERE user_id = userID OR $contacts.user_id$ = userID如果满足第一个条件，我想添加一个列，如:SELECT *,'type' as 'Inbox' FROM db.messages第二个条件:SELECT *,'type' as 'Send' FROM db.messages我还没有设法用 CASE...THEN 实现它
我会很感激任何评论。
SQL CASE 语句:

SELECT *,
CASE
    WHEN user_id = userID THEN 'Inbox'
    WHEN $contacts.user_id$ = userID THEN 'Send'
    ELSE NULL
END AS type
FROM db.messages;

Answer 1

case 语句的语法似乎无效，请检查 the documentation 。取而代之的是:

select
    case
        when a = x then 'a' as result
        when b = x then 'b' as result
        else null
    end as y
from table_name

试试这个:

select
    case
        when a = x then 'a'
        when b = x then 'b'
    end as 'result'
from table_name

甚至更简单:

select
    case x
        when a then 'a'
        when b then 'b'
    end as 'result'
from table_name