title: Non aggregate functions, relational algebra
body: <p>How can we translate the non aggregate functions of Structured Query Language into relational algebra expressions?! I know how to express the aggregate functions, but what about the non aggregate functions?! 
  e.g How can we write the Year( a date format column) function?! Just Year(date)?</p>
  
  <p>select e.name,year(e.dateOfEmployment) from Employees e</p>
  
  <p>Thanks!</p>