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Archives of the TeradataForum
Message Posted: Mon, 16 Aug 2004 @ 20:20:21 GMT
| Subj: | | Re: UNION And INSERT INTO |
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| From: | | Christie, Jon |
Even if the target table is initially empty, duplicate row checking will still have to be performed. Why? Because the UNION only guarantees
that there will be no duplicate rows for ALL COLUMNS. This does not guaranteed that some subset of columns (like the PI of the target table) will
be unique.
By the way, duplicate checking is only expensive where there are lots of duplicates. If it turns out that the spool really is unique on the PI
of the target table, the overhead for duplicate checking will very, very small.
Jon
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