with ... as sql
做用:指定臨時命名的結果集,相似於臨時表。express
可是,這個結果集被稱做:公用表表達式(CTE) - common_table_expressionide
能夠在select , insert , update , delete , merge語句的執行範圍定義。spa
公用表表達式能夠包括對自身的引用。因此,這種公用表表達式也稱爲遞歸公用表表達式。3d
語法:code
[ WITH <common_table_expression> [ ,...n ] ] <common_table_expression>::= expression_name [ ( column_name [ ,...n ] ) ] AS ( CTE_query_definition )
expression_name server
是公用表表達式的有效標識符。即名稱blog
column_name 遞歸
在公用表表達式中指定列名。ip
當在查詢定義中爲全部結果列都提供了不一樣的名稱時,列名是可選的。即此時能夠不寫。
CTE_query_definition
指定一個其結果集填充公用表表達式的 SELECT 語句。即查詢定義。
若是定義了多個 CTE_query_definition,則這些查詢定義必須用下列一個集合運算符聯接起來 :UNION ALL、UNION、EXCEPT 或 INTERSECT。
示例1
顯示每名銷售表明每一年的銷售訂單總數。
1.數據準備
create table SalesOrderHeader ( SalesPersonID varchar(50), SalesOrderID varchar(50), OrderDate varchar(50) ) --drop table SalesOrderHeader insert into SalesOrderHeader values ('01','20200330001','20200330') ,('02','20200330002','20200330') ,('02','20200331001','20200331')
2.使用
-- Define the CTE expression name and column list. WITH Sales_CTE (SalesPersonID, SalesOrderID, SalesYear) AS -- Define the CTE query. ( SELECT SalesPersonID, SalesOrderID, YEAR(OrderDate) AS SalesYear FROM SalesOrderHeader WHERE SalesPersonID IS NOT NULL ) -- Define the outer query referencing the CTE name. SELECT SalesPersonID, COUNT(SalesOrderID) AS TotalSales, SalesYear FROM Sales_CTE GROUP BY SalesYear, SalesPersonID ORDER BY SalesPersonID, SalesYear;
或
省略列名(在查詢中定義了列名)
-- Define the CTE expression name and column list. WITH Sales_CTE AS -- Define the CTE query. ( SELECT SalesPersonID, SalesOrderID, YEAR(OrderDate) AS SalesYear FROM SalesOrderHeader WHERE SalesPersonID IS NOT NULL ) -- Define the outer query referencing the CTE name. SELECT SalesPersonID, COUNT(SalesOrderID) AS TotalSales, SalesYear FROM Sales_CTE GROUP BY SalesYear, SalesPersonID ORDER BY SalesPersonID, SalesYear;
3.效果
示例2
如何在單個查詢中定義多個CTE
WITH Sales_CTE (SalesPersonID, TotalSales, SalesYear) AS -- Define the first CTE query. ( SELECT SalesPersonID, SUM(TotalDue) AS TotalSales, YEAR(OrderDate) AS SalesYear FROM Sales.SalesOrderHeader WHERE SalesPersonID IS NOT NULL GROUP BY SalesPersonID, YEAR(OrderDate) ) , -- Use a comma to separate multiple CTE definitions. -- Define the second CTE query, which returns sales quota data by year for each sales person. Sales_Quota_CTE (BusinessEntityID, SalesQuota, SalesQuotaYear) AS ( SELECT BusinessEntityID, SUM(SalesQuota)AS SalesQuota, YEAR(QuotaDate) AS SalesQuotaYear FROM Sales.SalesPersonQuotaHistory GROUP BY BusinessEntityID, YEAR(QuotaDate) ) -- Define the outer query by referencing columns from both CTEs. SELECT SalesPersonID , SalesYear , FORMAT(TotalSales,'C','en-us') AS TotalSales , SalesQuotaYear , FORMAT (SalesQuota,'C','en-us') AS SalesQuota , FORMAT (TotalSales -SalesQuota, 'C','en-us') AS Amt_Above_or_Below_Quota FROM Sales_CTE JOIN Sales_Quota_CTE ON Sales_Quota_CTE.BusinessEntityID = Sales_CTE.SalesPersonID AND Sales_CTE.SalesYear = Sales_Quota_CTE.SalesQuotaYear ORDER BY SalesPersonID, SalesYear;
示例1和示例2是非遞歸方式,示例3演示遞歸方式
示例3
示例3顯示經理以及向經理報告的僱員的層次列表。
1.數據準備
-- Create an Employee table. CREATE TABLE dbo.MyEmployees ( EmployeeID smallint NOT NULL, FirstName nvarchar(30) NOT NULL, LastName nvarchar(40) NOT NULL, Title nvarchar(50) NOT NULL, DeptID smallint NOT NULL, ManagerID int NULL, CONSTRAINT PK_EmployeeID PRIMARY KEY CLUSTERED (EmployeeID ASC) ); -- Populate the table with values. INSERT INTO dbo.MyEmployees VALUES (1, N'Ken', N'Sánchez', N'Chief Executive Officer',16,NULL) ,(273, N'Brian', N'Welcker', N'Vice President of Sales',3,1) ,(274, N'Stephen', N'Jiang', N'North American Sales Manager',3,273) ,(275, N'Michael', N'Blythe', N'Sales Representative',3,274) ,(276, N'Linda', N'Mitchell', N'Sales Representative',3,274) ,(285, N'Syed', N'Abbas', N'Pacific Sales Manager',3,273) ,(286, N'Lynn', N'Tsoflias', N'Sales Representative',3,285) ,(16, N'David',N'Bradley', N'Marketing Manager', 4, 273) ,(23, N'Mary', N'Gibson', N'Marketing Specialist', 4, 16);
2.遞歸使用演示
WITH DirectReports(ManagerID, EmployeeID, Title, EmployeeLevel) AS ( SELECT ManagerID, EmployeeID, Title, 0 AS EmployeeLevel FROM dbo.MyEmployees WHERE ManagerID IS NULL UNION ALL SELECT e.ManagerID, e.EmployeeID, e.Title, EmployeeLevel + 1 FROM dbo.MyEmployees AS e INNER JOIN DirectReports AS d ON e.ManagerID = d.EmployeeID ) SELECT ManagerID, EmployeeID, Title, EmployeeLevel FROM DirectReports ORDER BY ManagerID;
3.效果
示例4
下例演示在單個語句中包含兩個 CTE。 CTE 不能嵌套(無遞歸)
WITH CountDate (TotalCount, TableName) AS ( SELECT COUNT(datekey), 'DimDate' FROM DimDate ) , CountCustomer (TotalAvg, TableName) AS ( SELECT COUNT(CustomerKey), 'DimCustomer' FROM DimCustomer ) SELECT TableName, TotalCount FROM CountDate UNION ALL SELECT TableName, TotalAvg FROM CountCustomer;