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Message Posted: Fri, 31 Jan 2003 @ 11:00:49 GMT

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Subj:   Re: Query optimization: difference between inner join and derived table?
From:   Paul Johnson

Dave is right, as ever, but at a higher level than the mechanics involved, the queries are different in the question that is being asked.

The first will preserve the 1:1, 1:many, many:1 or many:many relationship between the two tables. The size of the result set depends on this relationship.

The second compares table 1 values to a distinct list of values in table 2 via a subquery. This is a constraint check on table 1 rather than a join between relations. The answer set can only be as large (or smaller) as the number of rows in table 1.

Paul Johnson.

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