I don’t really like nested case statements (if not required), and it looks like in this case you can simply assess each condition (assuming your conditions are mutually exclusive). This would help clean up the syntax confusion. I think you could do this:
case
when condition1 = 1 then 'result1'
when condition2 = 2 then 'result2'
when condition10 = 10 then 'result10'
end
This allows you to maintain your conditions and results list easily without worrying about nesting it even further. Do be aware it will assess the conditions in the order received.
(case when DMRHead.CheckOff3 = 1 then 'Prod'
else (case when DMRHead.CheckOff4 = 1 then 'PUR'
else (case when DMRHead.OutProcess_c = 1 then 'Outside'
else '' end ) end) end)