理想情况下,下面的代码应该输出一列中的男性数量和另一列中的女性数量。没有错误,但它只为男性创建一列,并将男性和女性的金额都放在该列下。
SELECT COUNT(Gender) AS Males FROM Customers
JOIN Rents ON Rents.Customers_Cid= Customers.Cid
JOIN Cars ON Cars.CarId=Rents.Cars_CarId
WHERE Make='Dodge' AND Gender='M'
UNION
SELECT COUNT(Gender) AS Females FROM Customers
JOIN Rents ON Rents.Customers_Cid= Customers.Cid
JOIN Cars ON Cars.CarId=Rents.Cars_CarId
WHERE Make='Dodge' AND Gender='F';
