hi
does anyone know if you are allowed to have the max/min functions in relational algebra?

i have this:
minSal:= sigma(min(eSalary))(employee);
getting the minimum salary of employees from employee table

then i have:
pi(eID, eFirst, eLast)(sigma(eSalary=minSal)(employee));
listing id and name of those employees whose salary matches my above relation - minSal

is this a proper use of min?

thanks,
gwog