What is projection operation in DBMS?

Projection operation (represented by $π$) belongs to relational algebra, which displays the specific column of a table mentioned in the query. It is a unary operationUnary operations are those which operate on one relation only. that returns its argument relation, with certain attributes left out.

Syntax

The syntax of projection is as follows:

Where A₁ and A₂ are attribute names and $r$ is a relation name.

The result is defined as the relation of $k$ columns obtained by erasing the columns that are not listed. It produces the output by removing the duplicate tuples from the table since relations are sets and sets do not have duplicates.

Example

Consider the following table (named Instructors) on which the projection operation would be applied:

If we want to get only the "Salary" column from the "Instructors" table, we'll perform the following command:

The above command would produce the following results:

Similarly, we can also project multiple columns from the table. If we want to display ID and their respective name (eliminate the "Salary" column), we'll perform the following operation:

The command would produce the following output:

Projection operation in SQL