On two articles we introduced the foreword to view query plan, and the way some common connection operator optimization techniques, this article, we summarize the joint operator of use and optimization techniques. BS, direct access to the theme of this Title. Based on the technical preparations Server2008R2 version SQL, using Microsoft a more compact case New Nike Free Run 3 Shoes Women Navy Womens database (Northwind) for resolution. A joint operator called joint operators, in fact, the most widely used on two kinds: UNION ALL and UNION. These operators usage is very simple, the former is the result of merging the two data sets, the latter is carried out to re-operations after the merger, if ever write T-SQL statements code farmers are not unfamiliar. Air Jordan 11 Red Mens Basketball Shoes We analyze these two operators display in the implementation plan, for example SELECT FirstName + N '' + LastName, City, Country FROM EmployeesUNION ALLSELECT ContactName, City, Country FROM Customers is above this Nike Zoom Lunarposite icon, this is the UNION ALL joint operator icon. This joint operator is very simple Reebok CL Chi Kaze operation, the two data sets will be scanned through a joint summary of the results. We look at this operator UNION, following the example select City, Country from EmployeesUNIONSELECT City, Country FROM Customers we can see, UNION operator is a Distinct Sort sort operation occurs after the concatenation operator, and after this operation will result collection to remove duplicate values. Air Max 2012 Green Orange Black We have always stressed: sorting large data table is a very resource intensive action! So, here New Nike Free 5.0 V4 Shoes Black Red we have found can be optimized option, remove the sort, or change the sort order. Replace mode Distinct Sort sequence sorting operation is Kazakhstan polymerization. Distinct Sort sorting operation requires the removal is proportional to the amount of data memory and repeat the previous set of data, and hash aggregation of memory required and the result set is removed after repeated proportional! So if a lot of duplicate values Nike Zoom KD V in the data row, then the comparison by hashing polymerization memory consumed will be less. Let's give an example select ShipCountry from OrdersUNIONSELECT ShipCountry FROM Orders This example is actually nothing useful here is to demonstrate that we look at the results we know that this list is that 653642-400 Blue Orange Lebron James Mens Basketball Shoes Nike Zoom Soldier VIII 8 there is a large area ShipCountry duplicate values, so the use of Kazakhstan Greek match come heavy operations are an optimal way. In fact, the phase matching connection 比哈希 way there is a more lightweight to heavy: the merge join an article I have analyzed this connection method for connection of two data sets, in fact, similar to here, the application before the original result must first set the sort! We know that can be used New Nike Free Run 3 Shoes Women Grey Purple Womens to optimize the way to improve the sorting speed indexing. Let's go heavy reproduce this way, we create a new table, and then create the index, as follows - New Table SELECT EmployeeID, FirstName + N '' + LastName AS ContactName, City, CountryINTO NewEmployeesFROM EmployeesGO-- add an index ALTER TABLE NewEmployees ADD CONSTRAINT PK_NewEmployees PRIMARY KEY (EmployeeID) CREATE INDEX ContactName ON NewEmployees (ContactName) CREATE INDEX ContactName ON CUSTOMERS (ContactName) GO-- New Query, there must Air Max 2012 Black Red White be a display of the Order by adding to appear to re-merge join SELECT ContactName FROM NewEmployeesUNION ALLSELECT ContactName FROM CustomersORDER BY ContactName way we can avoid the use of index scans explicit sort operation. We will change the UNION ALL UNION, the operation will be on the two datasets to re-operate. - New Query, there must be a display of the Order by adding to appear to re-merge join SELECT ContactName FROM NewEmployeesUNION SELECT ContactName FROM CustomersORDER BY ContactName UNION operation where we know the results will go to re-operate the above application Air Jordan Outlet flow aggregation operation , polymerization is generally applied to the packet flow operation, of course, it was used to re-grouped. In our actual application environment, the most common way to connect, or merge, but there is a situation most suitable for hash join, that is a small table and a Authentic Mens Basketball Shoes All Red Nike KD 7 Factory Outlet large table to conduct joint operations, which is particularly suitable for large table in the presence of a large number of duplicate values case. Hash algorithm is a good thing! References Microsoft Books Online Logical and Physical Operators Reference reference books 'SQL.Server.2005. Technology Insider' series Conclusion This article first this right, a little short, easy to understand and grasp, This 2015 Nike Free 5.0 part describes the query plan The combined operation of the operator, the next we analyze SQL Server in parallel computing, multi-core hyperthreading gathered today, look at SQL Server how to use parallel computing to maximize the use of existing hardware resources to enhance Air Jordan 14 Grey Red Womens performance, are interested in advance concern about the content of SQL Server performance tuning involves a wide range, follow-up article to expand the analysis in order. SQL Server software once deep inside, you'll find it really very deep, which can be described with very deep, if you want to study the inside of the tuning piece, you can focus on the content of this series, we study together! 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