What is the percentage of total orders from stores in Orange County in 2018?
DIVIDE(COUNT(OrderNumber where County = 'Orange County' and SUBSTR(OrderDate, -2) = '18'), COUNT(OrderNumber where SUBSTR(OrderDate, -2) = '18')) as percentage;
SELECT CAST(SUM(CASE WHEN T2.County = 'Orange County' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T1.OrderNumber) FROM `Sales Orders` AS T1 INNER JOIN `Store Locations` AS T2 ON T2.StoreID = T1._StoreID WHERE T1.OrderDate LIKE '%/%/18'