What were the total orders of Medsep Group from 2018 to 2020?
Medsep Group is the name of the customer; total orders refer to COUNT(OrderNumber); from 2018 to 2020 refers to SUBSTR(OrderDate, -2) IN ('18', '19', '20');
SELECT SUM(CASE WHEN SUBSTR(T1.OrderDate, -2) IN ('18', '19', '20') AND T2.`Customer Names` = 'Medsep Group' THEN 1 ELSE 0 END) FROM `Sales Orders` AS T1 INNER JOIN Customers AS T2 ON T2.CustomerID = T1._CustomerID