5.2 Joining Tables
A joined table is a composition of two tables that preserves a specified relationship between the participating tables (base tables).
The joined table contains all the columns from both base tables, but retains only the rows satisfying a specified join condition. The join condition is a relation between two columns, one from each base table. These two columns are called the join columns. The joined table can be thought of as the intersection of the two tables based on the join columns.
There are no restrictions on the nature of the base tables for joins, and joined tables can themselves be used in subsequent join operations. There is no limit to the number of tables that can be successively joined together in this way. Additionally, two tables can be joined together using multiple join conditions, that is, multiple pairs of join columns. This allows you to construct a joined table that embodies a very complex relation between the base tables.
The next sections explain how to create various types of joined tables.
See Also
What-If Analysis, for an illustration of using multiple join conditions.
Changing the Join Type, for information on converting between join types.
Editing a Composition Table, for Editable and Hierarchical modes of tables.
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