sql selecting unique rows based on a specific column

I have an table like this :

Col1    Col2    Col3    Col4
asasa   1          d    44
asasa   2         sd    34
asasa   3          f    3
dssd    4          d    2
sdsdsd  5         sd    11
dssd    1         dd    34
xxxsdsds2          d    3
erewer  3          sd   3

I am trying to filter out something like this based on Col1

Col1    Col2    Col3    Col4
asasa   1          d    44
dssd    4          d    2
sdsdsd  5         sd    11
xxxsdsds2          d    3
erewer  3         sd    3

I am trying to get the all unique rows based on the values in Col1. If I have duplicates in Col1, the first row should be taken.

I tried SELECT Col1 FROM tblname GROUP BY Col1 and got unique Col1 but extending it using * is giving me error.

Answer

You should be able to achieve your goal using something like the following:

WITH CTE AS (
    SELECT *, ROW_NUMBER() OVER (PARTITION BY Col1 ORDER BY Col2) AS rn FROM MyTable
)
SELECT * FROM CTE WHERE rn = 1

What it does is it creates a CTE (Common Table Expression) that adds a ROW_NUMBER on Col1, ordered by the data in row2.

In the outer select, we then only grab the rows from the CTE where the row number generated is 1.