Join two SQL tables with each other using two columns

Question

Problem:

I am trying to "translate" the id in two columns in a grading table (betyg_essays) to the real names of those users in another table (betyg_users).

The grading table (betyg_essays) look like this:

The user table (betyg_users) looks like this:

PHP code (so far):

$query = 'SELECT * FROM betyg_essays JOIN betyg_users ON betyg_essays.Examiner = betyg_users.UID';

Examiner/Supervisor columns (betyg_essays) correspond to the UID column (betyg_users).

Desired output should be (using the Firstname/Lastname columns):

1. Examiner: John Hopkins. Supervisor: Mike Baker.
2. Examiner: John Hopkins. Supervisor: Mike Baker.

Non-working SQL query:

$query = "SELECT 
            (u1.Firstname + ' ' + u1.Lastname) AS Examiner, 
            (u2.Firstname + ' ' + u2.Lastname) AS Supervisor
        FROM betyg_essays grade
            INNER JOIN betyg_users u1 ON grade.Examiner = u1.UID
            INNER JOIN betyg_users u2 ON grade.Supervisor = u2.UID";

Answer 1

SELECT
CONCAT(u1.FirstName, ' ', u1.LastName) AS Examiner,
CONCAT(u2.FirstName, ' ', u2.LastName) AS Supervisor
FROM betyg_essays e
INNER JOIN betyg_users u1 ON e.Examiner = u1.UID
INNER JOIN betyg_users u2 ON e.Supervisor = u2.UID

I didn't tried the code, you might need to make some adjustments.

UPDATE: Fixed the id's

INNER JOIN betyg_users u2 ON e.Supervisor = u2.UID

UPDATE2:

I have changed the + to CONCAT function. Apparently, MySQL handles string differently then SQL Server.

Answer 2

Here you need to join user_table two times first for getting examiner user name and second for supervisor username

SELECT (g1.FirstName + ' ' + g1.LastName) AS Examiner,' , (g2.FirstName + ' ' + g2.LastName) AS Supervisor
FROM grading_table grade
INNER JOIN user_table g1 ON grade.examiner = g1.uid
INNER JOIN user_table g2 ON grade.supervisor = g2.uid

Answer 3

Final solution:

$query = "SELECT 
            CONCAT (u1.Firstname, ' ', u1.Lastname) AS Examiner, 
            CONCAT (u2.Firstname, ' ', u2.Lastname) AS Supervisor
        FROM betyg_essays grade
            INNER JOIN betyg_users u1 ON grade.Examiner = u1.UID
            INNER JOIN betyg_users u2 ON grade.Supervisor = u2.UID";

Answer 4

Try this

SELECT CONCAT(betyg_users.`Firstname`," ",betyg_users.`Lastname`) AS `examiner_name`,
CONCAT(betyg_users.`Firstname`," ",betyg_users.`Lastname`) AS `superviser_name`
FROM `betyg_essays`
INNER JOIN `betyg_users` ON betyg_essays.`Examiner` = betyg_users.`UID` 
INNER JOIN `betyg_users` ON betyg_essays.`Supervisor` = betyg_users.`UID`;