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Oracle® PL/SQL® Interactive Workbook, Second Edition by Elena Silvestrova, Benjamin Rosenzweig

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JOINs

The 1999 ANSI standard introduced complete JOIN syntax in the FROM clause. The prior method was to list the tables needed in the query in the FROM clause and then to define the joins between these tables in the WHERE clause. However, the conditions of the SQL statement are also listed in the WHERE clause. It was decided to enhance this syntax because listing of the joins and the conditions in the same WHERE clause can be confusing.

The 1999 ANSI join syntax includes cross joins, equijoins, full outer joins, and natural joins.

CROSS JOINs

The CROSS JOIN syntax indicates that you are creating a Cartesian product from two tables. The result set of a Cartesian product is usually meaningless, but it can be used to generate a lot of rows if ...

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