SUM AND DIFFERENCE OF SQL code example

Example: sql group by sum

// Use SQL Group By clause after the Where clause
// Any column in the select list must either be in the Group By clause 
// or part of an agregation statement, like the Sum() statement
// Multiple columns can be included in the Group By Clause seperated by a comma
// Multiple columns stipulate the order tree. Order by 
// first column, then second ... etc

Select LastName, FirstName, Sum(LeaveDays), Max(age)
From EmployeeProjects
Where StartDate > '2020-01-01'
Group By LastName, FirstName