标签：temporary create after CTE select table SELECT view

Is it possible to create a temporary table in a View and drop it after select?

问题

I need to alter one view and I want to introduce 2 temporary table before the SELECT.

Is this possible? And how can I do it?

ALTER VIEW myView
AS 

SELECT *
INTO #temporary1

SELECT *
INTO #temporary2

SELECT * FROM #temporary1
UNION ALL 
SELECT * FROM #temporary1

DROP TABLE #temporary1
DROP TABLE #temporary2

When I attempt this it complains that ALTER VIEW must be the only statement in the batch.

How can I achieve this?

 

这玩意，应该直接在存储过程写

 

回答1

No, a view consists of a single SELECT statement. You cannot create or drop tables in a view.

Maybe a common table expression (CTE) can solve your problem. CTEs are temporary result sets that are defined within the execution scope of a single statement and they can be used in views.

Example (taken from here) - you can think of the SalesBySalesPerson CTE as a temporary table:

CREATE VIEW vSalesStaffQuickStats
AS
  WITH SalesBySalesPerson (SalesPersonID, NumberOfOrders, MostRecentOrderDate)
      AS
      (
            SELECT SalesPersonID, COUNT(*), MAX(OrderDate)
            FROM Sales.SalesOrderHeader
            GROUP BY SalesPersonID
      )
  SELECT E.EmployeeID,
         EmployeeOrders = OS.NumberOfOrders,
         EmployeeLastOrderDate = OS.MostRecentOrderDate,
         E.ManagerID,
         ManagerOrders = OM.NumberOfOrders,
         ManagerLastOrderDate = OM.MostRecentOrderDate
  FROM HumanResources.Employee AS E
  INNER JOIN SalesBySalesPerson AS OS ON E.EmployeeID = OS.SalesPersonID
  LEFT JOIN SalesBySalesPerson AS OM ON E.ManagerID = OM.SalesPersonID
GO

Performance considerations

Which are more performant, CTE or temporary tables?

 

 

Adding an INDEX to a CTE

回答1

I have had the same requirement. Indexes can not be added to a CTE. However, in the CTE select adding an ORDER BY clause on the joined fields reduced the execution time from 20 minutes or more to under 10 seconds.

(You need to also ADD SELECT TOP 100 PERCENT to allow an ORDER BY in a CTE select.)

[edit to add paraphrased quote from a comment below]:
If you have DISTINCT in the CTE then TOP 100 PERCENT doesn't work. This cheater method is always available: without needing TOP at all in the select, alter the ORDER BY statement to read:
ORDER BY [Blah] OFFSET 0 ROWS

 

回答2

No.

A CTE is a temporary, "inline" view - you cannot add an index to such a construct.

If you need an index, create a regular view with the SELECT of your CTE, and make it an indexed view (by adding a clustered index to the view). You'll need to obey a set of rules outlined here: Creating an Indexed View.

 

标签：temporary,create,after,CTE,select,table,SELECT,view
来源： https://www.cnblogs.com/chucklu/p/16396603.html

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