What is it your actually trying to do as there are various issues with your code. First, you have the problem as given by @Reeza, you are concatenating (a string function) numeric variables. Secondly, you are max()ing (a numeric function) on character data.
Provide a small bit of test data and show what you want out, maybe something like:
proc sql noexec;
select max(coalesce(SUTUN1,SUTUN2)) as CALCULATION
from (select * from BB2.OTT where D1="C" and D2="X");
quit;
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