Update SQL with a JOIN condition based on a case when - sas

Question

I have a dataset (BASE)with the following strucuture: a column with a index for every records, a column with a classification type, the classification value and a column i'd like to populate.
NAME |CLASSIFICATION|VALUE|STANDARD VALUE
FIDO |ALFABET |F |
ALFA |STANDARD |2 |
BETA |STANDARD |5 |
ETA |MIXED |B65 |
THETA|MIXED |A40 |
Not all records have the same classification, however I have an additional table (TRANSCODE) to convert the different classification methods into the standard one (which is classification):
ALFABET|STANDARD|MIXED
A |1 |A1
B |5 |A30
C |3 |A40
D |5 |A31
E |8 |B65
F |6 |C54
My goal is to populate the fourth column with the corresponding value i can find with the second table. (the records with the standard classification will have two columns with the same classification).
After that my data should be like the following:
NAME |CLASSIFICATION|VALUE|STANDARD VALUE
FIDO |ALFABET |F |6
ALFA |STANDARD |2 |2
BETA |STANDARD |5 |5
ETA |MIXED |B65 |8
THETA|MIXED |A40 |3
In order to do so i'm trying to do a proc sql update with a join condition but it doesn't seem to work
proc sql;
update BASE
left join TRASCODE
on BASE.VALUE= (
    case
        when BASE.CLASSIFCATION = 'ALFABET' then TRANSCODE.ALFABET 
        when BASE.CLASSIFICATION= 'STANDARD' then TRANSCODE.STANDARD
        when BASE.CLASSIFICATION= 'MIXED then TRANSCODE.MIXED
    end
)
set BASE.STANDARD_VALUE = TRANSCODE.STANDARD
;
quit;
Can someone help me?
Thanks a lot

Answer 1

The value selection for the standard value is a lookup query, so you can not join directly to transcode.
Try this UPDATE query that uses a different lookup selection for each classification:
data base;
infile cards missover;
input
NAME $ CLASSIFICATION $ VALUE $ STANDARD_VALUE $; datalines;
FIDO ALFABET F
ALFA STANDARD 2
BETA STANDARD 5
ETA MIXED B65
THETA MIXED A40
run;
data transcode;
input
ALFABET $ STANDARD $ MIXED $; datalines;
A 1 A1
B 5 A30
C 3 A40
D 5 A31
E 8 B65
F 6 C54
run;
proc sql;
update base
set standard_value =
case
when classification = 'ALFABET' then (select standard from transcode where alfabet=value)
when classification = 'MIXED' then (select standard from transcode where mixed=value)
when classification = 'STANDARD' then value
else 'NOTRANSCODE'
end;
%let syslast = base;