select column as true / false if id is exists in another table

问题:

I have 2 tables, one for members and another one for their services. Those are InnoDB tables on MySQL 5.6 server.

Members table:

id     |       name       |   phone ----------------------------------------   1       Daniel             123456789   2       Liam               123456789   3       Lucas              123456789 

Services table:

 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:

 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.

I tried to do it with JOINs and Sub-Queries without success, so I need your help ;)

回答1:

use LEFT JOIN Services table, Try this query

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2:

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3:

You can use a simple query like this

SELECT     m.id,     m.name     IF(s.MID,true,false) services FROM members m LEFT JOIN services s ON s.profile = m.id 

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