Natural Join

Combining Operations to Form Queries

If all we could do was to write single operations on one or two relations as queries, then relational algebra would not be as useful as it is. On the other hand, relational algebra, like all algebras, allows us to form expressions of arbitrary complexity by applying operators either to

Dependent and Independent Operations

Some of the operations that we have explained in previous sections can be expressed in terms of other relational-algebra operations. For instance, intersection can be expressed in terms of set difference:

Natural Joins / Outerjoins

As we recall from Natural Joins / Theta-Joins, a natural join differs from a theta-join in that: 1. The join condition is that all pairs of attributes from the two relations having a common name are equated, and there are no other conditions. 2. One of each pair of equated attributes is projected out.

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