how to tune sql query

In this article, the main description of the various connections in SQL and the scope of use, as well as the further interpretation of relational algebra and relational algorithms on the same query in different ways.Introduction to multi-table connectionsIn a relational database, a query tends to involve more than one table, because few have a single table, and i

------------------------------------------------------------------------------------------------------------------------Displays the disk activity volume generated by the transact-SQL statement.Set statistics Io on-- Disable the disk activity volume generated by the transact-SQL statement.Set statistics Io off-- Display [return detailed information about statement execution and estimate the resource require

the execution time of the algorithm is proportional to the square of the input size, the algorithm is called the logarithmic time algorithm. For a database, this means that the execution time of the query is proportional to the square of the database size.An example of a query with two times complexity is as follows:SELECT * from item, Authorwhere item.i_a_id=author.a_idThe minimum complexity is O (n log (

SQL query operation process and SQL operation processHere we can see the Query Processing of SQL in the book. In SQL, the query is achieved through the select statement and some auxilia

The first thing to note is that the content of this article is not how to tune SQL Server query performance (about which you can write a book), but how to leverage the set STATISTICS IO and set STATISTICS in SQL Server query performance tuning Time these two frequently ignor

algorithm is proportional to the square of the input size, the algorithm is called the logarithmic time algorithm. For a database, this means that the execution time of the query is proportional to the square of the database size.An example of a query with two times complexity is as follows:SELECT *from Item, Authorwhere item.i_a_id=author.a_idThe minimum complexity is O (n log (n)), but the maximum comple

sqlpassion Performance Tuning Training Planindividual study translation, if there is falsehood, please do not hesitate to point out, thank you. Week 1:sql Server How to execute a query　　Before we go into the intricacies of SQL Server performance tuning, I'd like to start by enumerating how SQL Server executes a

+ @WHERE -- ----Execution statistics EXEC sp_executesql @COUNTSQL, N ' @RECORDCOUNT INT out ', @RECORDCOUNT out -- ----Count pages SET @PageCount = CEILING (@RecordCount * 1.0/@PageSize) -- ----Query statement DECLARE @SQL NVARCHAR (2000) DECLARE @ORDERBY VARCHAR (100) SELECT @ORDERBY = ' ORDER by Tbsdinfo. Iscommon desc,tbsdinfo.commontime Desc,tbsdinfo. Createtime DESC ' IF (@PAGEINDEX =1

Date formatting statement and SQL Server statement during SQL Server Query The default datetime format of the Chinese version of SQL Server isyyyy-mm-dd Thh:mm:ss.mmm For example: select getdate() 2004-09-12 11:06:08.177 I sorted out the date format conversion methods that may be frequently used in

Article 1: how to optimize slow query SQL statements in MySQL56-Introduction to slow logs: in actual log analysis, there are usually a large number of slow logs, at the same time, there will be a large number of records for the same query. here we need to find the most problematic and optimized log in the actual log analysis, generally, the number of slow logs is

In programming languages with large numbers, the code is processed in the encoding order, but in SQL, the first clause to be processed is the FROM clause. Although the first SELECT statement appears, but it is almost always processed.Each step generates a virtual table, which is used as the input for the next step. These virtual tables are unavailable to callers (client applications or external queries. Only the table generated in the last step will b

Tags: databaseSQL databases T-SQL statement queryData files for attached databases650) this.width=650; "src=" https://s3.51cto.com/wyfs02/M01/96/06/wKiom1kcDfOB6lJHAAtJeP4PO9c190.jpg "style=" float : none; "title=" 1.jpg "alt=" Wkiom1kcdfob6ljhaatjep4po9c190.jpg "/>The category in the query table is the fruit of the factory date after 201-04-01650) this.width=650; "src=" Https://s3.51cto.com/wyfs02/M02/96/0

First of all, let's look at one of the steps here that translates into banner, which requires pivot, step-by-step Then look at the overall query results for the two query methods after the main table join So take a look at the latter query method is also through the industry after the conversion to do the join execution plan, you can see only the Word table

Recursive queries using CTE (common table expressions) ---- SQL Server 2005 and later versions A common table expression (CTE) has an important advantage: It can reference itself to create a recursive CTE. Recursive CTE is a public table expression that repeats the initial CTE to return a subset of data until the complete result set is obtained. When a query references recursive CTE, it is called recursive

Hibernate native SQL query Multiple table Association, SQL statement to pay attention to the problem@for ever 2009-9-4System environment:MySQL5.1Hibernate3.3The assumption is as follows:The entity classes Question and answer correspond to the data table Question and answer respectively.and the fields of table question and answer are mostly the same, and the numbe