Come trovare coppie univoche da due colonne in SQL?

preferirei usare concat e group by

SELECT 
col1,col2 
FROM 
tbl
GROUP BY CONCAT(LEAST(col1, col2), 
              GREATEST(col1, col2))

O SEMPLICEMENTE

SELECT 
    col1,col2 
    FROM 
    tbl
group by LEAST(col1, col2),GREATEST(col1, col2)