Question

I have a table called ‘bandsplusrating’ and a table called ‘ratings’
The table ‘bandsplusrating’ is filled with bands, the table ‘ratings’ starts empty.

Both tables have field called ‘naam’ with which they can be joined.
Table ‘ratings’ has a field called ‘fullname’

Multiple Ratings per band (bandsplusrating) will be stored in table ‘ratings’

Now i want to display all records from ‘bandsplusrating’ which havent been rated by a given user (ratings.fullname)

SELECT b.naam, b.stijl
FROM bandsplusrating b
LEFT JOIN ratings r ON b.naam = r.naam
WHERE r.fullname NOT LIKE 'Obama'

This query will still display a record when an other user has rated it.

Im am struggeling for days now, can someone assist me ?

Thanks!

Answer 1

Using NOT IN:

---

SELECT b.naam,
       b.stigl
  FROM BANDPLUSRATING b
 WHERE b.naam NOT IN (SELECT r.naam
                        FROM RATINGS r
                       WHERE r.fullname LIKE 'Obama')

Using NOT EXISTS:

---

SELECT b.naam,
       b.stigl
  FROM BANDPLUSRATING b
 WHERE NOT EXISTS(SELECT NULL
                    FROM RATINGS r
                   WHERE r.naam = b.naam
                     AND r.fullname LIKE 'Obama')

Using LEFT JOIN/IS NULL:

---

   SELECT b.naam,
          b.stigl
     FROM BANDPLUSRATING b
LEFT JOIN RATINGS r ON r.naam = b.naam
                   AND r.fullname LIKE 'Obama'
    WHERE r.naam IS NULL

Performance

---

Of the three options, the NOT IN and LEFT JOIN/IS NULL perform equally. NOT EXISTS doesn’t perform as well.