MySQL 如果 id 存在于另一个表中，则选择列为真/假
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/25284986/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
select column as true / false if id is exists in another table
提问by BeBest
I have 2 tables, one for members and another one for their services. Those are InnoDB tables on MySQL 5.6 server.
我有两张桌子，一张给会员，另一张给他们的服务。这些是 MySQL 5.6 服务器上的 InnoDB 表。
Members table:
成员表：
id | name | phone
----------------------------------------
1 Daniel 123456789
2 Liam 123456789
3 Lucas 123456789
Services table:
服务表：
MID | profile | lastSeen
----------------------------------------
1 2 2014-08-13 14:23:23
3 1 2014-08-12 15:29:11
I try to achieve this result:
我试图达到这个结果：
id | name | services
---------------------------------
1 Daniel true
2 Liam false
3 Lucas true
So if the user ID is exists in services table, the column services will be true or false otherwise.
因此，如果服务表中存在用户 ID，则服务列将是 true 或 false，否则。
I tried to do it with JOINs and Sub-Queries without success, so I need your help ;)
我试图用 JOIN 和子查询来做但没有成功，所以我需要你的帮助；)
回答by Girish
use LEFT JOINServices table, Try this query
使用LEFT JOIN服务表，试试这个查询
SELECT members.id, members.name,
IF(services.mid IS NULL, FALSE, TRUE) as services
FROM members
LEFT JOIN services ON (members.id = services.mid)
回答by Lennart
select m.id, m.name, case when s.mid is null then false else true end
from members m
left join services s
on s.profile = m.id
回答by Muhammad Raheel
You can use a simple query like this
您可以使用这样的简单查询
SELECT
m.id,
m.name
IF(s.MID,true,false) services
FROM members m
LEFT JOIN services s ON s.profile = m.id
