query to parse string

I have a table with two columns..

I am just displaying one record for brevity

COL_STR                                                  KEY
COL_A, COL_B, COL_C, COL_D                  COL_A

I need a query to process the above two values and return the following

return_val

TGT.COL_B = SRC.COLB
TGT.COL_C = SRC.COL_C
TGT.COL_D = SRC.COL_D

i would like the value in the key column to be excluded (in the above example COL_A)

if key has following
COL_A, COL_B

the output should be:

TGT.COL_C = SRC.COL_C
TGT.COL_D = SRC.COL_D

Please let me know if this is possible..

Thanks,