Distinct pair of values SQL

Question

Consider

 create table pairs ( number a, number b )  

Where the data is

1,1 1,1 1,1 2,4 2,4 3,2 3,2 5,1 

Etc.

What query gives me the distinct values the number column b has So I can see

1,1 5,1 2,4 3,2 

only

I've tried

select distinct ( a ) , b from pairs group by b  

but gives me "not a group by expression"

Answer 1

What you mean is either

SELECT DISTINCT a, b FROM pairs; 

or

SELECT a, b FROM pairs GROUP BY a, b; 

Answer 2

If you want to want to treat 1,2 and 2,1 as the same pair, then this will give you the unique list on MS-SQL:

SELECT DISTINCT      CASE WHEN a > b THEN a ELSE b END as a,     CASE WHEN a > b THEN b ELSE a END as b FROM pairs 

Inspired by @meszias answer above