來自查詢的單個SQL Server結果集

Question

請提供有關如何使用SQL Server 2005將兩個結果合並為一個的建議。

我遇到這樣的情況，一個Account最多可以有兩個Settlement Instructions ，其建模方式如下：

簡化模式：

Account
---------------------
Id
AccountName
PrimarySettlementId (nullable)
AlternateSettlementId (nullable)


SettlementInstruction
----------------------
Id
Name

我想要的輸出是一個帶有選擇語句的single result set ，其內容與此相似，這將允許我在Spring行映射器中構造一些Java對象：

select
  Account.Id as accountId, 
  Account.AccountName as accountName, 

  s1.Id as primarySettlementId, 
  s1.Name as primarySettlementName, 

  s2.Id as alternateSettlementId, 
  s2.Name as alternateSettlementName

我嘗試了各種方法，但是找不到找到將結果集合並到主FK和備用FK不為null的方法的方法。

最終，我搜索了該論壇，但似乎沒有什么適合我的需求。

Answer 1

您需要一個外部聯接 。

select
  Account.Id as accountId, 
  Account.AccountName as accountName, 

  s1.Id as primarySettlementId, 
  s1.Name as primarySettlementName, 

  s2.Id as alternateSettlementId, 
  s2.Name as alternateSettlementName
from Account
     left join SettlementInstruction s1 ON s1.Id = Account.PrimarySettlementId
     left join SettlementInstruction s2 ON s2.Id = Account.SecondarySettlementId
where /* ... */

Answer 2

你可以嘗試類似的東西：

SELECT
  a.Id as accountId, 
  a.AccountName as accountName, 
  'Primary' as Settlementtype
  s1.Name as primarySettlementName, 
FROM 
   Account a
INNER JOIN
   SettlementInstruction s1 ON a.PrimarySettlementId = s1.Id
UNION
SELECT
  a.Id as accountId, 
  a.AccountName as accountName, 
  'Alternate' as Settlementtype
  s2.Name as 'AlternateName', 
FROM 
   Account a
INNER JOIN
   SettlementInstruction s2 ON a.AlternateSettlementId = s2.Id

那對你有用嗎？

這會為您提供一個針對帳戶具有PrimarySettlementId的情況的所有帳戶/結算指令的列表，以及第二個備用帳戶不為空的帳戶/結算清單。 兩者均為NULL的將被省略。 某些Account實例可能重復（如果兩個ID字段均有效且不為null）。

或者，如果不是：您到底在尋找什么？