SQL Server equivalent of PostgreSQL distinct on ()

Question

I would like to have a Sql Server equivalent of the PostgreSQL distinct on ()

a  b
----
1  1
1  2
2  2
2  1
3  3

select distinct on (a) * 
from my_         


        

Answer 1

You can try ROW_NUMBER, but it can affect your performance.

;WITH CTE AS
(
    SELECT *, ROW_NUMBER() OVER(PARTITION BY a ORDER BY b) Corr
    FROM my_table
)
SELECT *
FROM CTE
WHERE Corr = 1

Answer 2

In addition to the accepted answer, you can avoid using two sentences and use a sub select like this

SELECT part.*
FROM (  SELECT *, ROW_NUMBER() OVER(PARTITION BY a ORDER BY b) Corr
    FROM my_table) part
WHERE part.Corr = 1