How to select DISTINCT rows without having the ORDER BY field selected

Question

So I have two tables students (PK sID) and mentors (PK pID). This query

SELECT s.pID
FROM students s JOIN mentors m ON s.pID = m.pID
WHERE m.tags LIKE \'%a%\         


        

Answer 1

Try this:

SELECT s.pID
FROM students s JOIN mentors m ON s.pID = m.pID
WHERE m.tags LIKE '%a%'
GROUP BY s.pID
ORDER BY s.sID DESC;

I.e. GROUP BY instead of DISTINCT should preserve order.