Question

Here’s the problems…

I have 4 tables: users, groups, users_groups, and emails. Note that users_groups references both the groups and users table. In other words, each time a user joins a group, the userId and groupId is entered into the users_groups table. A user can join multiple groups.

CREATE TABLE app.users (
`id` INT NOT NULL AUTO_INCREMENT ,
`firstName` INT NOT NULL ,
`lastName` INT NOT NULL ,
PRIMARY KEY (`id`)
) ENGINE = InnoDB;

CREATE TABLE app.groups (
`id` INT NOT NULL AUTO_INCREMENT ,
`groupName` VARCHAR(32) NOT NULL ,
PRIMARY KEY (`id`)
) ENGINE = InnoDB;

CREATE TABLE app.users_groups (
`id` INT NOT NULL AUTO_INCREMENT ,
`userId` INT NOT NULL ,
`groupId` INT NOT NULL ,
PRIMARY KEY (`id`)
) ENGINE = InnoDB;

CREATE TABLE app.emails (
`id` INT NOT NULL AUTO_INCREMENT ,
`userId` INT NOT NULL ,
`email` VARCHAR(32) NOT NULL ,
PRIMARY KEY (`id`)
) ENGINE = InnoDB;

Now I would like to query these tables and display the result like this:

 +---------+-------------------+--------------+
 |name     |emails             |groups        |
 +---------+-------------------+--------------+
 |John Doe |[e-mail],  |group1,group2,|
 |         |[e-mail]  |group3        |
 +---------+-------------+---------+----------+

Answer 1

You could use group_concat for that:

select  concat(u.Firstname, ' ', u.Lastname) as name
,       group_concat(distinct e.email separator ',') as emails
,       group_concat(distinct g.groupName separator ',') as groups
from    users u
left join
        users_groups ug
on      ug.userId = u.id
left join
        groups g
on      g.Id = ug.GroupId
left join
        emails e
on      e.UserId = u.Id
group by
        u.Id
,       u.Firstname
,       u.Lastnmae