Question

我从来没有做过这样的事情，我尝试在谷歌上找到它但没有结果。

我有3个表格如下：

订单

OdredID (int) PK,
UserID (int) FK,
OdredDate (datetime)

组件：

ComponentID (int) PK,
Name (nvarchar(50)),
Type (nvarchar(max))

OrderComponent：

OrderComponentID (int) PK,
OrderID (int) FK,
ComponentID (int) FK,
Value (nvarchar(max))

假设一个订单有3个组件，其名称为：[CPU, Motherboard, Memory]和值[1GHz, AsusP5, 2GB Kingston DDR3]

我需要一个像这样的列的结果：

OrderID  UserID   Date          CPU    Motherboard   Memory
   1        1     2012-05-21    1GHz   AsusP5        2GB Kingston DDR3

基本上我需要每个连接行作为新列，其名称取自联接表的Name列和Value列的值。

Answer 1

试试这个：

SELECT
  o.orderid,
  o.userid,
  MAX(CASE WHEN c.Name = 'CPU' THEN oc.Value END) AS 'CPU',
  MAX(CASE WHEN c.Name = 'Motherboard' THEN oc.Value END) AS 'Motherboard',
  MAX(CASE WHEN c.Name = 'Memory' THEN oc.Value END) AS 'Memory'
FROM orders o
INNER JOIN ordercomponents oc ON c.orderid = oc.orderId
INNER JOIN Components c ON oc.componentid = c.componentid
GROUP BY o.orderid, o.userid

SQL Fiddle Demo

请注意：这是执行此操作的标准SQL方法。但您可以使用SQL Server PIVOT表运算符执行相同的操作：

SELECT  *
FROM
(
   SELECT o.orderid, o.userid, c.Name 'Name', oc.value 'value'
   FROM orders o
   INNER JOIN ordercomponent oc ON o.orderid = oc.orderId
   INNER JOIN Components c ON oc.componentid = c.componentid
 ) t 
PIVOT
(
  MAX(value)
  FOR Name IN ([CPU], [Motherboard], [Memory])
) p;

但这适用于一组预先定义的值，例如[CPU], [Motherboard], [Memory]。

对于未知数量的值，您必须动态执行此操作：

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

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

set @query = 'SELECT orderid, userid  ' + @cols + ' from 
             (
                 select o.orderid, o.userid, c.Name Name, oc.value value
                 FROM orders o
                 INNER JOIN ordercomponent oc ON o.orderid = oc.orderId
                 INNER JOIN Components c ON oc.componentid = c.componentid
            ) x
            pivot 
            (
                max(value)
                for name in (' + @cols + ')
            ) p '

execute(@query);

根据join中的值将联接结果添加为新列

1 个答案:

SQL Fiddle Demo

Updated SQL Fiddle Demo