Question

我将尝试在Ticket和Membership之间使用左外连接。但是，它不会在Ticket上显示NULL值的外键。你能给我一些答案吗？这个查询有什么问题吗？感谢。

FROM Ticket t, Production pro, Performance per, Price, Price_level, Booking, Customer, Customer_Concession ccons, Membership, Member_concession mcons
WHERE t.performanceid = per.performanceid AND
  t.PRODUCTIONID = Price.PRODUCTIONID AND
  t.levelId = Price.levelId AND
  Price.PRODUCTIONID = pro.PRODUCTIONID AND
  Price.levelId = Price_level.levelId AND
  Booking.bookingId (+) = t.bookingId AND
  Customer.customerId = Booking.customerId AND
  ccons.cConcessionId (+) = Customer.cConcessionId AND  
  Membership.membershipId (+) = t.membershipId AND
  Membership.mConcessionId = mcons.mConcessionId 
ORDER BY t.ticketId

Answer 1

您遇到的一个潜在问题是这两个条件：

  Booking.bookingId (+) = t.bookingId AND
  Customer.customerId = Booking.customerId AND

由于您正在对Booking进行外部联接，因此当找不到匹配项时，其列将显示为NULL;但随后你正常加入Customer，所以这些行将被删除，因为NULL不能等于任何东西。您可能还想将第二行更改为外连接。

但是，我不知道这是否是你的主要问题，因为我实际上并不确切地理解你在问什么。 “外键的NULL值”是什么意思？您尚未指定外键是什么。

Answer 2

为了扩展Dave的观察，并给你一个SQL92语法的例子，请学习它并远离Oracle自己的外连接语法。

FROM
TICKET t
JOIN Performance per
ON per.performance_id = t.performance_id
JOIN Production pro
ON pro.produciton_id = t.production_id
JOIN PRICE pr
ON pr.production_id = pro.production_id
AND pr.levelId = t.level_id
JOIN price_level pl
ON   pl.levelid = pr.levelid
LEFT OUTER JOIN booking b
on  b.booking_id = t.booking_id
LEFT OUTER JOIN customer cus
on  cus.customer_id = b.customer_id
LEFT OUTER JOIN customer_concession cons
ON cons.concession_id = cus.concession_id
LEFT OUTER JOIN memebership m
ON M.membership_id = t.membership_id
LEFT OUTER JOIN membership_concession mc
ON mc.mConcession_id = m.mConcession_id
Order by t.ticketid

Oracle SQL开发人员如何显示外键的NULL值

2 个答案: