在SQL Server查詢中多次顯示一列

Question

我需要一些SQL查詢的幫助。我有兩個表和ENDPOINT。對於每個用戶，在ENDPOINT表中例如定義了3行。

USER ENDPOINT  ENDPOINTTYPE 
123 123456  HomePhone 
123 456789  CellPhone 
123 A@gmail.com Email 

我想在單行顯示這些數據，例如

USER HomePhone CellPhone Email 

你能告訴我一個方法來達到這個目的嗎？

非常感謝！

Answer 1

嘗試是這樣的：

SELECT 
    U.[User], 
    EP1.EndPoint as 'HomeEndpoint', EP1.Endpotintype as 'HomeEndpointType', 
    EP2.EndPoint as 'CellEndpoint', EP2.Endpotintype as 'CellEndpointType', 
    EP3.EndPoint as 'EmailEndpoint', EP3.Endpotintype as 'EmailEndpointType' 
FROM Users U 
    LEFT JOIN EndPoint EP1 ON U.[User] = EP1.[User] AND EP1.EndPointType = 'HomePhone' 
    LEFT JOIN EndPoint EP2 ON U.[User] = EP2.[User] AND EP2.EndPointType = 'CellPhone' 
    LEFT JOIN EndPoint EP3 ON U.[User] = EP3.[User] AND EP3.EndPointType = 'Email' 

還是要回到剛纔的4列：

SELECT 
    U.[User], 
    EP1.EndPoint as 'Home Phone', 
    EP2.EndPoint as 'Cell Phone', 
    EP3.EndPoint as 'Email' 
FROM Users U 
    LEFT JOIN EndPoint EP1 ON U.[User] = EP1.[User] AND EP1.EndPointType = 'HomePhone' 
    LEFT JOIN EndPoint EP2 ON U.[User] = EP2.[User] AND EP2.EndPointType = 'CellPhone' 
    LEFT JOIN EndPoint EP3 ON U.[User] = EP3.[User] AND EP3.EndPointType = 'Email' 

這裏是SQL Fiddle - 注意，我換柱用戶到用戶id，因爲它是一個保留字（或者你可以使用括號）。

Answer 2

這種類型的數據轉換被稱爲樞軸。 SQL Server有啓動與SQL Server 2005

之前到SQL Server 2005中的旋轉功能，這可以使用聚合函數與CASE表達來完成：

select [user], 
    max(case when ENDPOINTTYPE = 'HomePhone' then EndPoint end) HomePhone, 
    max(case when ENDPOINTTYPE = 'CellPhone' then EndPoint end) CellPhone, 
    max(case when ENDPOINTTYPE = 'Email' then EndPoint end) Email 
from yourtable 
group by [user]; 

見SQL Fiddle with Demo。

如果您正在使用SQL Server 2005+，然後轉動查詢看起來像：

select * 
from 
(
    select [user], endpoint, endpointtype 
    from yourtable 
) src 
pivot 
(
    max(endpoint) 
    for endpointtype in (HomePhone, CellPhone, Email) 
) piv 

見SQL Fiddle with Demo

上述查詢工作的偉大，如果你提前知道時間的價值。如果你沒有，那麼你將要使用動態SQL：

DECLARE @cols AS NVARCHAR(MAX), 
    @query AS NVARCHAR(MAX) 

select @cols = STUFF((SELECT distinct ',' + QUOTENAME(ENDPOINTTYPE) 
        from yourtable 
      FOR XML PATH(''), TYPE 
      ).value('.', 'NVARCHAR(MAX)') 
     ,1,1,'') 

set @query = 'SELECT [USER],' + @cols + ' from 
      (
       select [USER], [ENDPOINT], [ENDPOINTTYPE] 
       from yourtable 
      ) x 
      pivot 
      (
       max(ENDPOINT) 
       for ENDPOINTTYPE in (' + @cols + ') 
      ) p ' 

execute(@query) 

見SQL Fiddle with Demo

所有的查詢返回相同的結果：

| USER | HOMEPHONE | CELLPHONE |  EMAIL | 
---------------------------------------------- 
| 123 | 123456 | 456789 | A@gmail.com |