# Relational Algebra - Select Operator (Selection) - $\sigma$

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

## Visualisation

select vs project

## Notation

• 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

$$\LARGE \sigma_{(color='Blue')} Shirts$$

• SQL Notation
SELECT * FROM Shirts WHERE color='Blue'