5.2. Basic Operations in the Relational Model

According to Codd's theory, several operations on a relational model are defined. These operations are one fundamental of relational databases. Knowing these operations will help you to understand what your database does internally:

  • SELECT— This operation is used to extract a list of tuples from a table. These tuples have to fulfill certain conditions in order to be selected.

  • PROJECT— To retrieve certain columns from a relation, a PROJECT operation has to be performed.

  • PRODUCT— PRODUCT builds the Cartesian product of two tables. Whenever a join is performed, the database will (at least theoretically) compute the Cartesian product of two objects. After that the result will in most cases be reduced to ...

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