無法連接表

Question

我試圖編寫一個查詢來顯示每個乘客的名字與他們的票價。 這裏是我到目前爲止什麼 - 它給沒有錯誤，也沒有任何結果：

-- Write a query to display the Name of each passenger as well as the fare for their trip. 
select passenger.name, departure_info.fare * passenger.quantity AS passenger_fare 
from passenger, seat_passenger, manages, departure_info, seat_info 
where departure_info.Dept_id=manages.Dept_id 
AND manages.Seat_id=seat_info.Seat_id 
AND seat_info.Seat_id=seat_passenger.Seat_id 
AND seat_passenger.Pass_id=passenger.pass_id 

下面是使用正確的聯接語法，會使這個查詢從您的查詢的表http://i.imgur.com/R4EFthY.png

Answer 1

的關係圖

select 
    p.name, di.fare * p.quantity as passenger_fare 
from passenger as p 
    inner join seat_passenger as sp on sp.pass_id = p.pass_id 
    inner join seat_info as si on si.seat_id = sp.seat_id 
    inner join manages as m on m.seat_id = si.seat_id 
    inner join departure_info as di on di.dept_it = m.dept_id 

我建議你把inner joins爲left outer joins，看看你錯過了什麼

select 
    p.name, di.fare * p.quantity as passenger_fare, 
    sp.pass_id, si.seat_id, m.seat_id, di.dept_id 
from passenger as p 
    left outer join seat_passenger as sp on sp.pass_id = p.pass_id 
    left outer join seat_info as si on si.seat_id = sp.seat_id 
    left outer join manages as m on m.seat_id = si.seat_id 
    left outer join departure_info as di on di.dept_it = m.dept_id 

事實上，你甚至可以刪除未使用的連接（如果你沒有錯過seat_info一些記錄）：

select 
    p.name, di.fare * p.quantity as passenger_fare 
from passenger as p 
    inner join seat_passenger as sp on sp.pass_id = p.pass_id 
    inner join manages as m on m.seat_id = sp.seat_id 
    inner join departure_info as di on di.dept_it = m.dept_id