How do I (or can I) SELECT DISTINCT on multiple columns?

Question

I need to retrieve all rows from a table where 2 columns combined are all different. So I want all the sales that do not have any other sales that happened on the same day f

Answer 1

I want to select the distinct values from one column 'GrondOfLucht' but they should be sorted in the order as given in the column 'sortering'. I cannot get the distinct values of just one column using

Select distinct GrondOfLucht,sortering
from CorWijzeVanAanleg
order by sortering

It will also give the column 'sortering' and because 'GrondOfLucht' AND 'sortering' is not unique, the result will be ALL rows.

use the GROUP to select the records of 'GrondOfLucht' in the order given by 'sortering

SELECT        GrondOfLucht
FROM            dbo.CorWijzeVanAanleg
GROUP BY GrondOfLucht, sortering
ORDER BY MIN(sortering)