Something I'm missing in minus set operation...

We have a table here used by a web app to determine columns for particular tables. The table is out of sync with the actual columns in the tables. To determine which columns should be removed from the table I wrote the following:

Select distinct(trim(col_name))
>From owner.col_dim

Minus
Select distinct(trim(column_name))
>From sys.all_tab_columns;

...but that is yielding the wrong results. What am I missing? The datatypes are the same. ...i don't even think I should need the trim in there but that too yields wrong results.

? ....it is very early here so I have somewhat of an excuse.

Thanks
chris=20

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