Question

我想要的结果是关于一个订单的信息。当我的订单有一些订单时，下面的查询工作正常，但一旦它是一个空的订单它不提供任何信息。例如我的orderid = 5，而且这个还没有任何项目。我使用orderitems来计算订单的总成本。如果没有订购，我如何获取我的信息？这是我的查询：

SELECT DISTINCT 
  u.firstname|| ' ' || u.lastname, 
  TO_CHAR(o.date,'DD-MON-YY HH24:mm'),
  (SELECT SUM(oItem.amount * oItem.pricewhenordered) FROM ORDERITEM oItem WHERE 
  oItem.ORDERID=o.ID), 
  (case o.employeeid
    when null then '-'
    else (SELECT us.firstname|| ' ' || us.lastname FROM user us WHERE 
    id=o.employeeid)
  END), 
  o.status
FROM order o, orderitem oItem, user u
WHERE o.userid = u.id
AND o.id = oItem.orderid
AND o.id = 5;

TABLES
order ID，用户身份，日期，状态， employeeid

orderitem 订单ID，产品ID，量， pricewhenordered

user ID，用户名，密码，名字，姓， usertypeid

Answer 1

明确你的联接并在没有项目的情况下使用LEFT联接应该可以胜任。

SELECT DISTINCT 
  u.firstname|| ' ' || u.lastname, 
  TO_CHAR(o.date,'DD-MON-YY HH24:mm'),
  (SELECT SUM(oItem.amount * oItem.pricewhenordered) FROM ORDERITEM oItem WHERE 
  oItem.ORDERID=o.ID), 
  (case o.employeeid
    when null then '-'
    else (SELECT us.firstname|| ' ' || us.lastname FROM user us WHERE 
    id=o.employeeid)
  END), 
  o.status
FROM order o
LEFT OUTER JOIN orderitem oItem ON  o.id = oItem.orderid
INNER JOIN user u ON o.userid = u.id
WHERE o.id = 5;

Answer 2

您实际上并未在主查询中使用ORDERITEM（oitem）表;把它留下来：

SELECT DISTINCT 
  u.firstname|| ' ' || u.lastname, 
  TO_CHAR(o.date,'DD-MON-YY HH24:mm'),
  (SELECT SUM(oItem.amount * oItem.pricewhenordered) 
     FROM ORDERITEM oItem 
    WHERE oItem.ORDERID=o.ID), 
  (case o.employeeid
        when null 
        then '-'
        else (SELECT us.firstname|| ' ' || us.lastname 
                FROM user us 
               WHERE id=o.employeeid)
        END), 
  o.status
FROM 
    order o, user u
WHERE 
    o.userid = u.id
    AND o.id = 5;

没有订单商品的sql订单不会给出结果

2 个答案: