sql - transform and group data together -

from query retrieve information need results this:

code | category ----------- 1    |  1    |  2    |  b 3    |  b 3    |  b 4    |  b 

from data following result:

combination 1&2 | combination 3&4 --------------------------------- 'both & b'    |  'just b" 

so happening is, if first column takes rows code 1 or 2. sees if in these rows:

-are rows equal category result in value "just a"

-are rows equal category b result in value"just b"

-is there mix of categories , b's codes 1 , 2 result in value"both & b".

this again happen inside of second column except codes 3&4. in practice combining many codes of these column, columns combine 2 codes, other can combine 10 codes, , on. trying see category combination of codes are. a's, b's, or @ mixed?

you can use conditional aggregation:

select (case when min(category) <> max(category) 'both , b'              when min(category) = 'a' 'a only'              when min(category) = 'b' 'b only'          end) t code in (1, 2) , category in ('a', 'b');