duplicate key insert

When inserting into a table using a select from another table and creating an error with a duplicate key, is it possible to find the value of the key that was duplicated?

better to use a loop likeSTART THE LOOP:

• read the record
• check if key exists
• if not insert
• if yes write to table PROBLEMATIC_RECS
• IS THIS LAST RECORD IF YES EXIT

GO TO START THE LOOPDo something like this with PL/SQL or PHP or PRO*C