Question

3 tables are defined as follows:

Users

User_ID      INT
First_Name   VARCHAR
Last_Name    VARCHAR
Email        VARCHAR

Roles

Role_ID      INT
Role_Name    VARCHAR
Access_Level INT

Roles_Users

User_ID      INT
Role_ID      INT

Roles_Users is a many-to-many linking table between Users and Roles. I want to pull back the following info:

First_Name, Last_Name, Email, Role_Name

What I have so far is:

SELECT 
    U.First_Name,
    U.Last_Name,
    U.Email,
    R.Name AS Role_Name
FROM Users U
INNER JOIN Roles_Users RU ON U.User_ID = RU.User_ID
INNER JOIN Roles R ON RU.Role_ID = R.Role_ID

The tricky part (at least for me) is that I want to only pull back the Role_Name with the MIN(Access_Level) for that particular user. So basically the record set I want to pull will have each user only listed once with their lowest access level role name.

I’m sure this is pretty simple but it’s just stumping me right now.

Thanks

Answer 1

YOu can use a CTE (Common Table Expression) in conjunction with the ROW_NUMBER windowing function like this:

;WITH MinAccessData AS
(
SELECT 
    U.First_Name,
    U.Last_Name,
    U.Email,
    R.Name AS Role_Name,
    ROW_NUMBER() OVER(PARTITION BY U.User_ID ORDER BY R.Access_Level) AS RowNum
FROM Users U
INNER JOIN Roles_Users RU ON U.User_ID = RU.User_ID
INNER JOIN Roles R ON RU.Role_ID = R.Role_ID
)
SELECT *
FROM MinAccessData
WHERE RowNum = 1

The CTE “partitions” your data by User_ID, e.g. each user gets a “partition”. Inside that partition, the roles are ordered by Access_level and the smallest is the first one – so it gets RowNum = 1 – for each user.

So you then select from that CTE all those entries where the RowNum = 1 – this delivers all the entries for each user which have the smallest Access_Level value.