Relational Algebra

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Essentially a mathematical system that allows us to manipulate relations/tables through a series of operations.

Behind the scenes, SQL transforms queries into relational algebra in order to retrieve results.

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Consists of;

• operands: relations/variables representing relations
• operators: map relations to other relations
• rules for combining operands/operators into expressions
• rules for evaluating these expressions.

Set Operations

Selection — Sel[expr](Rel)

Projection — Proj[A,B](Rel)

Rename — Rename[schema](Rel)

Union — R1 Union R2

Intersection — R1 Intersect R2

Difference — R1 - R2

Cartesian Product — R1 x R2

Natural Join — R1 Join R2

Theta Join — R1 Join[cond] R2

Division — R1 Div R2