query postgres for distinction across two columns

Question

i have a database with the following table

Col1 | Col2 | Col3  |  
 A   | C     | data1
 A   | B     | data2
 B   | A     | data3
 A   | D     | data4
 C   | A     | data5

I need a query that will select all distinct rows across Col1 and Col2 (So AC == CA), but I need to count the total.

So my return might be like

Combo| Count
AC | 2
AB | 2
AD | 1

Answer 1

This looks like a simple aggregation query with a twist because the ordering is not important:

select least(col1, col2) || greatest(col1, col2), count(*) as cnt
from t
group by least(col1, col2) || greatest(col1, col2);