SELECT DISTINCT pair of COLUMN in SQL

Question

Consider

create table pairs ( number a, number b )

Where the data is

1,4
4,1
2,4
2,4
3,2
3,2
2,3
5,1
Etc.

I'm Getting this

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

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

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

only

I don't want the value in column a should be present in column b. Please help.

what i need is to select distinct values on both sides of column. for eg. if (1,2) is present then (2,1) must not be present

Answer 1

You didn't state your DBMS, but this works on many DBMS (least and greatest aren't part of the SQL standard unfortunately)

select distinct least(a,b), greatest(a,b)
from pairs