问题描述
我必须编写一条select语句,该语句显示一个表中的orderId和交货地址,但是如果没有交货地址,它应该显示客户的帐单地址。我不确定如何执行此操作,因为UNION需要相同数量的列。
这是两个表:
CREATE TABLE CUSTOMER (
CustId number(4) NOT NULL,CFirstName varchar2(30),CSurname varchar2(30),BillingAddr varchar2(30),Gender varchar2(1),PRIMARY KEY (CustId),CONSTRAINT Check_CGender
CHECK (CGender IN ('M','F'))
);
CREATE TABLE SHOPORDER (
OrdId number(4) NOT NULL,DeliveryAddress varchar2(30),CustId number(4),SpId number(4),PRIMARY KEY (OrdId),CONSTRAINT FK_CustId
FOREIGN KEY (CustId) REFERENCES CUSTOMER,CONSTRAINT FK_SpId
FOREIGN KEY (SpId) REFERENCES SALESPERSON
);
这是问题的措辞: 使用UNION子句列出每个订单ID和地址。该列表必须在 升序ID顺序。如果车间订单交货地址为NULL, 那么您必须显示客户的帐单邮寄地址,而不是送货地址。
任何帮助都非常有用。
我目前的尝试哈哈
SELECT Ordid,DeliveryAddress
FROM SHOPORDER
UNION
SELECT NULL AS CustId,BillingAddr
FROM CUSTOMER;
SELECT S.OrdId,S.DeliveryAddress
FROM SHOPORDER S
UNION
SELECT S.OrdId,C.BillingAddr
FROM CUSTOMER C
INNER JOIN SHOPORDER S
ON C.CustId = S.CustId;
SELECT S.OrdId
FROM SHOPORDER S
INNER JOIN CUSTOMER C
ON S.CustId = C.CustId;
(SELECT DeliveryAddress
FROM SHOPORDER
UNION
SELECT BillingAddr
FROM CUSTOMER );
SELECT OrdId,DeliveryAddress
FROM SHOPORDER
UNION
SELECT BillingAddr
FROM CUSTOMER;
SELECT OrdId,(SELECT DeliveryAddress
FROM SHOPORDER
UNION
SELECT BillingAddr
FROM CUSTOMER)
FROM SHOPORDER;
解决方法
您正在寻找LEFT JOIN
和COALESCE()
:
select so.OrdId,coalesce(so.DeliveryAddress,c.BillingAddr) as address
from shoporder so left join
customer c
on so.CustId = c.CustId;