Tuesday, September 29, 2009

Pseudo-Cartestian Products

A Cartestian Product is what you get when you (accidentally) don't specify a where clause in the join between two tables in an RDBMS. It is the product of all rows in T1 times all rows in T2. You only get them if you completely forget to join two tables. It happens, but rarely. What is much more common is a flawed join, where you get a product between a subset of rows in each table, because you aren't using enough columns in the join.

We need a term for "imperfect join which results in a large number of rows, some of which are 'synthesized' and carry data which does not actually exist in the base tables".

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