SQL Distinct Pair Groupings -


i interested in manipulating data so:

my source data:

from | | rate ---------------- eur  | aud | 1.5895 eur  | bgn | 1.9558 eur  | gbp | 0.7347 eur  | usd | 1.1151 gbp  | aud | 2.1633 gbp  | bgn | 2.6618 gbp  | eur | 1.3610 gbp  | usd | 1.5176 usd  | aud | 1.4254 usd  | bgn | 1.7539 usd  | eur | 0.8967 usd  | gbp | 0.6589

in regards "distinct pairs", consider following "duplicates".

eur | usd matches usd | eur eur | gbp matches gbp | eur gbp | usd matches usd | gbp

i want source data filtered such removes 1 of above "duplicates", such final table 3 records less original. not care record "duplicates" kept or removed, long 1 selected.

i have tried many variations of joins, exists, except, distinct, group by, logical comparisons (< >) , feel close given approach... not seem click.

my favorite effort has involved inner joining on except:

select a.[from], a.[to], a.[rate] table inner join (   select distinct [from], [to]   table    except   (     select [to] [from], [from] [to]     table    ) ) b on a.[from] = b.[from] , a.[to] = b.[to]

but alas, removes of matched pairs.

i can suggest easy, if doesn't matter 1 of want, can pick 1 rate bigger 1 or on contrary 1 smaller. each pare should 1 rate bigger , 1 smaller (make sense) 

select * table rate>1

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