Question

Lets say I have 2 tables:

1 with users
and another one which keeps record of which users used what codes.

Users
-----
Id, Name
1, 'John'
2, 'Doe'

Codes
------
Id, UserId, code
1, 1, 145
2, 1, 187
3, 2, 251

Now I want to pull a query that results he following

Name, UsedCodes
'John', '145,187'
'Doe', '251'

How can this be done with a query or stored procedure?

Answer 1

Since you haven’t specified the DB I’m giving you two options:

MySql

With MySql you should simply use GROUP_CONCAT() aggregate function.

Microsoft SQL Server 2005+

Obviously the fastest way (no cursors, no coalesce…) of getting the same result on MS DB is by using FOR XML PATH('') that simply omits XML elements.

SELECT
    u.Name,
    c1.UserId,
    (
        SELECT c2.Code + ','
        FROM Codes c2
        WHERE c2.UserId = c1.UserId
        ORDER BY c2.code
        FOR XML PATH('')
    ) as Codes
FROM Codes c1
    JOIN Users u
    ON (u.Id = c1.UserId)
GROUP BY c1.UserId, u.Name

Other alternatives

Read this article, that explains all the possible ways of achieving this goal.