sql server 2008 - How to select distinct combinations of 2 rows in sql -


how select distinct combinations of 2 rows.

eg. given following table

col1 col2     b     b     c c     b b

i want select 

col1 col2      b      c c      b

note using distinct key word not work include last row b,a.

i don't want last row returned because reverse combination (a,b) in set. 

select t1.col1,t1.col2 table t1 col2 not in (select t2.col1 table t2 t2.col2 = t1.col1) group t1.col1,t1.col2

or 

select distinct t1.col1, t1.col2 table t1 col2 not in (select t2.col1 table t2 t2.col2 = t1.col1)

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