PROJECT (Relational Algebra)

The PROJECT operation, $\pi$, is used to keep certain columns (attributes) from a relation and discard all others. PROJECT uses vertical partitioning, the list of specified columns is kept in each tuple, other attributes in each tuple are discarded. Duplicate rows are removed since relations are sets.

$${\pi }_{<\text{attribute list}>}(R)$$

Where $\pi$ denotes the PROJECT operator. Where $<\text{attribute list}>$ denotes the desired list of attributes from $R$. Where $R$ denotes the relation.

Example:

• Select the employee’s first name, last name, and salary: ${\pi }_{\text{LNAME, FNAME, SALARY}}(EMPLOYEE)$

Properties:

• The number of tuples in the result of a projection ${\pi }_{<\text{list}>}(R)$ is always less or equal to the number of tuples in $R$.