// 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

SELECT CityID, 

       COUNT(*) NumberOfDogsInThisCity,

       SUM(CASE WHEN DogName = 'Tedy' THEN Wheight ELSE 0 END) WheightOfAllDogWithNameTedy

FROM Dogs

GROUP BY CityID