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

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Visualisation

select vs project

Notation

This can be read as:

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

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'