Question

I’m struggling with the right type of conditional select statement here, even after searching.

I have a table with users. Some are owners, some are just guests, like so:

TABLE A 
UserID    | UserType | Directory | RegisteredToID | Name
1         | Guest    |           | 3              | Bob
2         | Guest    |           | 3              | Susan
3         | Owner    | abc       | (null)         | Charles
4         | Guest    |           | 20             | Hugh
etc...

I’m trying to get one query statement that results the Bob, Susan, and Charles records with the directory name showing for each, like so:

Name    | Directory
Bob     | abc
Susan   | abc
Charles | abc

In other words, Bob and Susan are guests of Charles, but Charles’ record contains the directory name I want. Hope my question makes sense?

EDIT: I should have mentioned this twist….I won’t know the directory name, just a userID (e.g. 1 for Bob) and am trying to retrieve the correct directory name to associate for each user, whether they are a guest or not. Only owner records have a directory name filled in.

Answer 1

You need to join the table on itself and decide with CASE which Directory to select.

Out of my head (don’t have access to a SQL Server at the moment):

SELECT
    t1.Name,
    CASE WHEN t1.RegisteredToID is null
        THEN t1.Directory 
        ELSE t2.Directory 
    END AS Directory
FROM 
    TableA AS t1
LEFT JOIN TableA AS t2 
    ON t1.RegisteredToID = t2.UserID