Renaming attribute

$$ \rho_{Y \leftarrow X}R $$

Example 1:

Collect all the IDs in university

$\rho_{student \leftarrow SIds} \cup \rho_{Professor \leftarrow ProfIds}$

Example 2:

Projection, Selection

Selection

Filter some tuples on the base of Property $F$

$\sigma_F(R)$ \\sigma_F(R)where

• $F$ is cardinality depends on the property

• $R$ is schema

Projection

Produce results over a subset of the attributes of the operand, with values from all its tuples

$\pi_Y(R)$ \\pi_Y(R) where

• Given a relation $R(X)$, $Y$ is a subset of X

• $R$ is schema

Example:

$\sigma_{\texttt{Country="IT"}}(Student)$