SQL Server 2005 CTE学习总结
SQL Server 2005引入了一个很有价值的Tracsact-SQL组件：通用表表达式（Common Table Expression,CTE）,它是一个可以由定义语句引用的临时命名的结果集，类似于引用派生表和视图的方式。1，简单的使用
USE AdventureWorks;
GO
--DirReps为CTE的名字，包含两个字段
WITH DirReps(ManagerID, DirectReports) AS
(
SELECT ManagerID, COUNT(*)
FROM HumanResources.Employee AS e
WHERE ManagerID IS NOT NULL
GROUP BY ManagerID
)
--返回表DirReps的内容
SELECT ManagerID, DirectReports
FROM DirReps
ORDER BY ManagerID;
GO
USE AdventureWorks;
GO
WITH Sales_CTE (SalesPersonID, NumberOfOrders, MaxDate)
AS
(
SELECT SalesPersonID, COUNT(*), MAX(OrderDate)
FROM Sales.SalesOrderHeader
GROUP BY SalesPersonID
)
--这里我们再一次的使用了CTE Sales_CTE
SELECT E.EmployeeID, OS.NumberOfOrders, OS.MaxDate,
E.ManagerID, OM.NumberOfOrders, OM.MaxDate
FROM HumanResources.Employee AS E
JOIN Sales_CTE AS OS
ON E.EmployeeID = OS.SalesPersonID
LEFT OUTER JOIN Sales_CTE AS OM
ON E.ManagerID = OM.SalesPersonID
ORDER BY E.EmployeeID;
GO
2，递归应用
利用CTE对一个表进行排序那是相当简单，我之前写过一个排序的例子，现在想想感觉很可笑。在同一个表内显示数据分级
--创建原表
create table #test
(
id int,
level int,
pid int,
sortorder int
)
--插入数据,假定有三级数据
insert into #test select 1,0,0,1
insert into #test select 2,1,1,2
insert into #test select 3,0,0,3
insert into #test select 4,1,3,4
insert into #test select 5,0,0,5
insert into #test select 6,1,1,6
insert into #test select 7,2,4,7
go
--排序前
SELECT * FROM #test
go
--排序后
WITH CTE
AS
(
SELECT *,cast('0' AS nvarchar(max)) + cast(ROW_NUMBER() OVER(PARTITION BY pid ORDER BY pid)AS nvarchar(20)) AS newsortorder FROM #test WHERE level = 0
UNION ALL
SELECT t.*,(c.newsortorder + CAST(ROW_NUMBER() OVER(PARTITION BY t.pid ORDER BY t.pid) AS nvarchar(max))) AS newsortorder
FROM #test t
INNER JOIN CTE c ON t.pid = c.id
)
SELECT * FROM CTE ORDER BY newsortorder
go
DROP TABLE #test
参考：使用SQL2005 递归查询结合Row_Number()实现完全SQL端树排序
作者：冰碟
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