query to parse string

what version of the db?  Full 4-digit version please  like 11.2.0.1   not 11g

This should work in 10.2.0.1 and above
I made the assumption that you would have 10 columns or less.  If that's not true, simply bump up the LEVEL <= 10 to something large enough to accomodate your data


SELECT 'TGT.' || str || ' = ' || 'SRC.' || str
  FROM (SELECT REGEXP_SUBSTR(
                   col_str,
                   '[^ ,]+',
                   1,
                   n
               )
                   str
          FROM yourtable,
               (    SELECT LEVEL n
                      FROM DUAL
                CONNECT BY LEVEL <= 10)
         WHERE REGEXP_SUBSTR(
                   col_str,
                   '[^ ,]+',
                   1,
                   n
               )
                   IS NOT NULL
        MINUS
        SELECT REGEXP_SUBSTR(
                   key,
                   '[^ ,]+',
                   1,
                   n
               )
          FROM yourtable,
               (    SELECT LEVEL n
                      FROM DUAL
                CONNECT BY LEVEL <= 10)
         WHERE REGEXP_SUBSTR(
                   key,
                   '[^ ,]+',
                   1,
                   n
               )
                   IS NOT NULL)

You're always doing a great job here at EE, sdstuber. But I think it would be nice, if you might explain your (awesome) SQL statements a bit more to the asker (so they may learn better to use and adept).
Just a thought ;-) Keep going!

Kind regards,
Alex