Question

I sort the rows on date. If I want to select every row that has a unique value in the last column, can I do this with sql?

So I would like to select the first row, second one, third one not, fourth one I do want to select, and so on.

Answer 1

What you want are not unique rows, but rather one per group. This can be done by taking the MIN(pk_artikel_Id) and GROUP BY fk_artikel_bron. This method uses an IN subquery to get the first pk_artikel_id and its associated fk_artikel_bron for each unique fk_artikel_bron and then uses that to get the remaining columns in the outer query.

SELECT * FROM tbl 
WHERE pk_artikel_id IN
  (SELECT MIN(pk_artikel_id) AS id FROM tbl GROUP BY fk_artikel_bron)

Although MySQL would permit you to add the rest of the columns in the SELECT list initially, avoiding the IN subquery, that isn’t really portable to other RDBMS systems. This method is a little more generic.

It can also be done with a JOIN against the subquery, which may or may not be faster. Hard to say without benchmarking it.

SELECT * 
FROM  tbl
  JOIN (
    SELECT 
      fk_artikel_bron, 
      MIN(pk_artikel_id) AS id
    FROM tbl
    GROUP BY fk_artikel_bron) mins ON tbl.pk_artikel_id = mins.id