多个连接语句未返回预期结果

时间:2011-03-12 03:58:49

标签: sql join

我必须编写一个符合以下要求的查询:

  

查询应该返回所有的列表   名为的客户的条目值   “史蒂夫”和显示的每个日期(如果   可用)最新的状态详细信息   那个日期。

客户表

CustomerID | CustomerName
1          |    Steve
2          |    John

条目表

CustomerID | EntryDate | EntryValue 
 1         | 5/4/2010  |    200.0  
 1         | 4/4/2010  |    100.0  
 1         | 3/4/2010  |    150.0
 1         | 2/4/2010  |    170.0
 2         | 5/4/2010  |    220.0

状态表

CustomerID | StatusDate | Detail
1          | 5/28/2010  | D
1          | 4/24/2010  | S
1          | 4/5/2010   | P
1          | 2/28/2010  | A

预期输出为:

CustomerName |   Date    |   OrderCost |   Detail 
  Steve      | 5/4/2010  |    200.0    |  S
  Steve      | 4/4/2010  |    100.0    |  A
  Steve      | 3/4/2010  |    75.0     |  A
  Steve      | 3/4/2010  |    75.0     |  <null>

我认为预期的输出可能是错误的,实际应该是:

CustomerName |   Date    |   OrderCost |   Detail 
  Steve      | 5/4/2010  |    200.0    |  S
  Steve      | 4/4/2010  |    100.0    |  A
  Steve      | 3/4/2010  |    150.0     |  A
  Steve      | 2/4/2010  |    170.0     |  <null>

根据要求,我不明白为什么2010年3月4日的日期会发生两次,第二次会有详细信息。我写了以下查询:

我写了以下查询:

SELECT  Customers.CustomerName, Entries.EntryDate, Entries.EntryValue, Status.Detail
FROM   Customers
    INNER JOIN Entries ON Customers.CustomerID = Entries.CustomerID
    LEFT OUTER JOIN Status ON Status.CustomerID = Customers.CustomersID AND Status.StatusDate <= Entries.EntryDate
WHERE (Customers.CustomerName = 'Steve')

我的查询结果如下:

CustomerName| EntryDate |   EntryValue |   Detail
Steve      |  5/4/2010 |    200.00  |   S
Steve      |  5/4/2010 |    200.00  |   P
Steve      |  5/4/2010 |    200.00  |   A
Steve      |  4/4/2010 |    100.00  |   A
Steve      |  3/4/2010 |    150.00  |   A
Steve      |  2/4/2010 |    170.00  |   NULL

我在这里做错了什么提示?我无法弄明白......

更新 我已将订单更改为条目,因此不会让我们感到困惑。

4 个答案:

答案 0 :(得分:1)

您获得的结果超出预期,因为状态表中的许多行都满足第二个JOIN条件(例如,有5个状态日期早于5/4,因此此日期在结果集中出现3次)。

您需要加入状态表,但只能获得一个匹配(最新)。这可以通过几种方式完成,AFAIK通常带有子查询。我认为你的情况相当复杂 - 我使用临时表。希望它有所帮助......(我目前没有数据库来测试它,希望没有愚蠢的语法错误。)

DROP TABLE IF EXISTS temp;

CREATE TABLE temp AS  -- This temp table is basically the result set you got
 (SELECT c.CustomerName, e.EntryDate, e.EntryValue, s.Detail, s.StatusDate
  FROM Customers c
    INNER JOIN Entires e ON c.CustomerID = e.CustomerID
    LEFT OUTER JOIN Status s ON s.CustomerID = c.CustomersID
                    AND s.StatusDate <= e.EntryDate
  WHERE (c.CustomerName = 'Steve')
 );

SELECT t.CustomerName, t.EntryDate, t.EntryValue, t.Detail
FROM temp t
WHERE t.StatusDate = (SELECT MAX(t2.StatusDate) 
                      FROM temp t2 
                      WHERE t2.EntryDate = t.EntryDate);

要避免创建临时表,我相信这会有用(请尝试让我知道!)

SELECT t.CustomerName, t.EntryDate, t.EntryValue, t.Detail
FROM (SELECT c.CustomerName, e.EntryDate, e.EntryValue, s.Detail, s.StatusDate
      FROM Customers c
      INNER JOIN Entries e ON c.CustomerID = e.CustomerID
      LEFT OUTER JOIN Status s ON s.CustomerID = c.CustomersID
                      AND s.StatusDate <= e.EntryDate
      WHERE c.CustomerName = 'Steve') AS t
WHERE t.StatusDate = (SELECT MAX(t2.StatusDate)
                      FROM temp t2
                      WHERE t2.EntryDate = t.EntryDate);

答案 1 :(得分:1)

您可以使用子查询来获取状态 对于SQL Server使用TOP 1,对SQLite / MySQL使用LIMIT 1

SQL Server / SyBase

SELECT Customers.CustomerName, Entries.EntryDate, Entries.EntryValue,
   (SELECT top 1 Status.Detail From Status
    where Status.CustomerID = Customers.CustomersID AND Status.StatusDate <= Entries.EntryDate
    order by Status.StatusDate desc)
FROM   Customers
INNER JOIN Entries ON Customers.CustomerID = Entries.CustomerID
WHERE (Customers.CustomerName = 'Steve')

MySQL / SQLite

SELECT Customers.CustomerName, Entries.EntryDate, Entries.EntryValue,
   (SELECT Status.Detail From Status
    where Status.CustomerID = Customers.CustomersID AND Status.StatusDate <= Entries.EntryDate
    order by Status.StatusDate desc
    limit 1)
FROM   Customers
INNER JOIN Entries ON Customers.CustomerID = Entries.CustomerID
WHERE (Customers.CustomerName = 'Steve')

答案 2 :(得分:0)

状态日期是否应该在订单日期之后?类似的东西:

SELECT  Customers.CustomerName, Orders.OrderDate, Orders.OrderCost, Status.Detail
FROM   Customers
    INNER JOIN Orders ON Customers.CustomerID = Orders.CustomerID
    LEFT OUTER JOIN Status ON Status.CustomerID = Customers.CustomersID 
WHERE Customers.CustomerName = 'Steve' AND Status.StatusDate >= Orders.OrderDate

此外,CustomerID表中的Status似乎有点奇怪,因为它通常是具有状态的订单,而不是客户。状态表不应该有OrderID字段吗?

答案 3 :(得分:0)

预期输出错误。最后一行应该是2010年2月4日。此外,他们的订单成本也不对。 2/4/2010应该返回null,因为没有匹配状态。