Relational Algebra - Select Operator (Selection) - <math>\sigma</math>

1 - About

The select operator is a relational operator that select the rows of a relation.

3 - Visualisation

select vs project

4 - Notation

This can be read as:

  • Keep rows that satisfy the condition c (ie predicate)
  • Delete rows that fail the condition c (ie predicate)

5 - Example

Select the shirts that satisfy the condition color=blue

  • Relational Algebra Notation

<MATH> \LARGE \sigma_{(color='Blue')} Shirts </MATH>

  • SQL Notation

SELECT * FROM Shirts WHERE color='Blue'

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