MINUS: spool both tables & redistribute -> sort distinct -> exclusion merge join

Is the table SET or MULTISET? If it's MULTISET you'll need MINUS ALL, if it's SET, then MINUS ALL is more efficient, too.

MINUS ALL: spool both tables & redistribute -> sort -> minus all join

But spooling & redistributing is a large overhead, so if it's a SET table the most efficient way is probably using
NOT EXISTS: just a direct exclusion merge join

Of course it's easier to code a
SEL * FROM T1 MINUS ALL SEL * FROM T2
instead of a
SEL * FROM T1
WHERE NOT EXISTS
(SEL * FROM T2 WHERE T1.col1 = T2.col2 AND ... T1.col50 = T2.col50)
but it's probably worth the effort (and you can create the code using dbc.columns)

Dieter