You can write an expression and place it in the SELECT list of a SQL Query.
For example , you want to display the Total Leaves available for the user from the Employee table. Total Leaves in this case can be VacationHours + SickLeaveHours.
Below is the Query include the expression as column and display the results.
SELECT VacationHours + SickLeaveHours AS Leaves FROM HumanResources.Employee;