davejuk — 2011-03-01T08:59:28-05:00 — #1
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!
r937 — 2011-03-01T09:02:45-05:00 — #2
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 — 2011-03-01T09:08:38-05:00 — #3
Wow - 3 minutes... I see why your avatar is a clock now!
Thanks for your help. Very much appreciated.
system — 2011-03-01T16:51:49-05:00 — #4
You can accomplish this with a denormalization query... I've written a detailed blog on how to do this here:
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.
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
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