Returning values as field names

[davejuk]

Hi

This isn't the easiest problem to describe but I'll do my best...

I have 3 tables, with the field names in brackets;

UserAccounts (ID, UserNick, Pass)
UserRoles (ID, Description)
UserAccountRoles (UserAccountID, UserRoleID)

I use these to define the roles of each user (and therefore the permissions they have) within my application. I want to construct a query to return each user in one column, followed by columns for each role containing a boolean value indicating whether or not they are in this role (i.e. whether a record exists in the UserAccountRoles table).

I can do something like this to get a list but it's not the most user friendly way of presenting it to the user:

SELECT UserAccounts.ID, UserAccounts.UserNick, UserRoles.Description FROM ((UserAccounts LEFT JOIN UserAccountRoles ON UserAccounts.ID = UserAccountRoles.UserAccountID) LEFT JOIN UserRoles ON UserAccountRoles.UserRoleID = UserRoles.ID) ORDER BY UserAccounts.UserNick

I generally get on pretty well with SQL but I can't even figure out where to get started with this one! Is it even possible? Any help greatly appreciated!

Regards,

Dave

[r937]

it is possible but only if you hard-code all the roles

this type of layout is called a crosstab, and it is much better to do it in the application layer than in sql

[davejuk]

Wow - 3 minutes... I see why your avatar is a clock now!

Thanks for your help. Very much appreciated.

[transio]

You can accomplish this with a denormalization query... I've written a detailed blog on how to do this here:

http://www.transio.com/content/how-d...able-using-sql

The basic requirement is that you need a finite number of properties to display as columns.

Here's an example of how your query might look using your schema:

Obviously, you'll have to change "ROLEx" for the names of your roles.

Cheers!

SELECT 
    ua.ID,
    MAX(CASE WHEN st.name = 'ROLE1' THEN 1 ELSE 0 END) AS ROLE1,
    MAX(CASE WHEN st.name = 'ROLE2' THEN 1 ELSE 0 END) AS ROLE2,
    MAX(CASE WHEN st.name = 'ROLE3' THEN 1 ELSE 0 END) AS ROLE3,
    MAX(CASE WHEN st.name = 'ROLE4' THEN 1 ELSE 0 END) AS ROLE4
FROM
    UserAccounts AS ua
    INNER JOIN UserAccountRoles AS uar ON ua.ID = uar.UserAccountID
    INNER JOIN UserRoles AS AS ur ON ur.ID = uar.UserRoleID
GROUP BY ua.ID