Relational Algebra

Relational algebra is the basic set of operations for the relational model. These operations enable a user to specify basic retrieval requests (queries). The result of an operation is a new relation, which may have been formed from one or more input relations. Hence can be further manipulated.

Relational Algebra Expression

A sequence of relational algebra operations forms a relational algebra expression.

We may choose to use single expressions or a sequence of operations:

• $${\pi }_{\text{FNAME, LNAME, SALARY}}({\sigma }_{DNO=5}(EMPLOYEE))$$
• $$\begin{array}{rl}DEP5\_EMPS& \leftarrow {\sigma }_{DNO=5}(EMPLOYEE)\\ RESULT& \leftarrow {\pi }_{\text{FNAME, LNAME, SALARY}}(DEP5\_EMPS)\end{array}$$

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