Question

我需要查询以下语句：

显示为客户预订超过4辆汽车租赁的所有员工的详细信息。

架构如下：

Staff (staffID, firstname, lastname, xyz..)

Customers (customerID, firstname, lastname, xyz..)

Booking (bookingID, staffID, customerID, vehicleregistration, date)

Vehicle (vehicleregistration, make, model, xyz..)

干杯！

Answer 1

我认为所有预订记录是客户的实际车辆租赁。所以你想要计算每个员工。 每位员工转换为GROUP BY staffid。要检查汇总结果（计数），请使用HAVING子句。

select * 
from staff
where staffid in
(
  select staffid
  from booking
  group by staffid
  having count(*) > 4
);

如您所见，无需加入任何内容，因为您只需要员工表中的数据。预订计数是最好属于WHERE条款的标准。

为了完整起见，这里有一个连接：

select s.* 
from staff s
join
(
  select staffid
  from booking
  group by staffid
  having count(*) > 4
) b on b.staffid = s.staffid;

我发现这种可读性较差，但有些人可能更喜欢它。如果您希望在结果中显示聚合中的信息，则可以使用此选项，在您的情况下是计数。

select s.*, b.bookings
from staff s
join
(
  select staffid, count(*) as bookings
  from booking
  group by staffid
  having count(*) > 4
) b on b.staffid = s.staffid;

Answer 2

SELECT staffID,COUNT(vehicleregistration) FROM Staff JOIN Booking ON Staff.staffID = Booking.staffID JOIN Vehicle ON Vehicle.vehicleregistration = Booking.vehicleregistration GROUP BY staffID HAVING COUNT(vehicleregistration) > 4

SQL连接和聚合函数

2 个答案: