For two tables ‘Employees’ and ‘Sales’, if we want to get total sales done by employee with a specific employee name.

Employees table

EmployeeID, EmployeeFirstName, EmployeeLastName, EmployeeEmailID, EmployeeContactNo

Sales table

SalesID, SalesEmployeeID, SalesDate, SalesTotal

The requirement can be fulfilled by the below 2 SQL statement. What is the performance difference between these three.

SELECT COUNT(SalesTotal), SUM(SalesTotal)  FROM Sales  WHERE SalesEmployeeID = (SELECT EmployeeID FROM Employees WHERE EmployeeFirstName = 'GIVEN')  SELECT COUNT(SalesTotal), SUM(SalesTotal)  FROM Sales s INNER JOIN Employees e ON s.SalesEmployeeID = e.EmployeeID  WHERE e.EmployeeFirstName = 'GIVEN'  SELECT COUNT(SalesTotal), SUM(SalesTotal)  FROM Sales s, Employees e  WHERE s.SalesEmployeeID = e.EmployeeID AND e.EmployeeFirstName = 'GIVEN'