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Message Posted: Thu, 19 Jan 2006 @ 11:11:26 GMT

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Hi Vijay,

1) Those three terms are very similar. "cross join" (a) is the ANSI syntax name for what is often referred to as an "unconstrained product join" (which is a "cartesian join" - c) . The number of rows in the output (spool file in Teradata terms) is the product of the number of qualifying rows in each of the two inputs. Think of "cross join" as a "join type", it provides a certain piece of functionality (not used often in business queries).

A "product join" is a join strategy, i.e. what type of processing the DBMS is going to use to answer your query. Even if you code an INNER or OUTER join in your SQL, you may well find that the optimiser chooses a product join as the processsing mechanism. The number of rows in the output of a "product join" will be the product of the qualifying rows in each of the inputs, where the join criteria are met.

Cheers,

Dave

Ward Analytics Ltd: Information in motion ( www.ward-analytics.com )

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