query tuning in sql server

Brief introduction In SQL Server, an index is an enhanced existence, which means that SQL Server can still implement functionality even without indexes. However, indexes can greatly improve query performance in most cases, especially in OLAP. To fully understand the concept

To analyze the performance of a query, you can view {Tagshow (event, '% D6 % B4 % D0 % D0 % BC % C6 % BB % AE ');} "Href =" javascript:; "target =" _ Self ">Execution Plan. Execution Plan description {Tagshow (event, 'SQL ');} "Href =" javascript:; "target =" _ Self ">SQL{Tagshow (event, 'server ');} "Href =" javascrip

First SQL statementSelect CompanyName GSMC,ZB Zhibiao from Left Join T_companycode on T_GSNDZB.GSBH=T_companycode.companyidQuery Result:A second SQL statementSELECT min(CompanyName) GSMC,cast(round(sum(T_xstj.hsje)/10000,2) asNumeric -,2)) Ndje fromT_xstj Left JoinT_companycode onT_companycode.companyid=T_XSTJ.GSBHwhere DateDiff( YearSjgetdate())=0 Group byGsbhQuery Result:Statements that are merged int

Usage scenarios:For example, you need to query all student numbers with scores greater than 95, separated by commas into a string, from the Student score table.To prepare the test data:CREATE TABLE score (ID int,score int)INSERT into score values (1,90)INSERT into score values (2,96)INSERT into score values (3,99)It is now necessary to query the result string "2,,3" with a single statement.The

groupedSuch as:-The total number of girls and boys receivedSelect Sex,count (*) from Student GROUP by sexOrder of Query statements:Select from where the group by has an order byNote: Where is the filter for the source data. It can only use columns that are referred to in the table following the fromAn aggregate function cannot be used after a where condition, and an error will be made if usedHavingIf you are filtering the result set after grouping, t

=n ' Ms_description ', @value =n ' table notes ', @level0typE=n ' SCHEMA ', @level0name =n ' dbo ', @level1type =n ' table ', @level1name =n ' name ' EXEC sp_updateextendedproperty @name =n ' Ms_ Description ', @value =n ' table Notes ', @level0type =n ' SCHEMA ', @level0name =n ' dbo ', @level1type =n ' table ', @level1name =n ' name '/*** Query comment Related sql***********************/--view table Comm

SQL random Query SQL Server: Select Top N * from Table order by newid () The newid () function creates a unique value of the uniqueidentifier type. The preceding statement reads N records randomly from the table. MySQL: Select * from Table order by rand () limit 10 STR converts a number to a string for compa

Today, when writing a program, you need to generate an SQL statement from the start ID to the end ID. It turns out that you don't need this feature now. How do you query SQL Server for data SQL statements that are queried between the first few to several in the database?For

Ind_attribute.is_ Disabled as [is disabled] 4 from (5 select Tab_name,index_name, [Co_names]=stuff ((SELECT ', ' +[co_name ') from 6 (select Tab. Name as Tab_name,ind. Name as index_name,col.name as Co_name from sys.indexes IND 7 INNER JOIN Sys.tables tab on Ind. object_id = tab.object_id and Ind.type in (8) inner join sys.index_columns index_columns on tab.object_id = Index_colu mns.object_id and ind.index_id = index_columns.index_id 9 inner join sys.columns Col on tab.object_id = col.object_i

Label:--Paging data----row_number () is called window-opening function, can be paged operation Select Row_number () over (order by ID) as Num,*from gb_data----adds a sequential num value to each column to facilitate the use of the first few data. Select row_number () over (order by ID) as num,* from Gb_data where Num>5and num 10--This line of code is wrong, because the system does not recognize how much num is, why? -Because of the order of execution, the

The word booksearch may be unfamiliar to many developers. Many people have encountered this word, but they have not paid enough attention to it, so they have always ignored its existence. The word booksearch may be unfamiliar to many developers. Many people have encountered this word, but they have not paid enough attention to it, so they have always ignored its existence. The growth of SQL Server Cognit

(TRUE ), when the write lock is performed, all Query Cache related to the table will be invalidated. If it is set to 0 (FALSE), the Query Cache related to the table can still be read at the lock time. 3. Query Cache and Performance Nothing is too late, especially for systems with frequent writes, enabling the Query Ca

The growth of SQL Server Cognition 1. I don't have to graduate or work for a long time. I only know the relationship between SQL and SQL Server Oracle and MySql. I usually think that SQL is S