how to optimize sql query using execution plan

fields are letters plus numbers, you can try the pure numbers, letters, characters, and so on, understand how the next mmsql will change the SQL statement to take advantage of the index. And then try again what is a nonclustered index? With no index and what about? Subquery How is MSSQL executed? in with no index, like with no index? function with no index? or,and,UNION? What about subqueries? Here I do not try to show you, as long as you know how t

SQL profile is a SQL statement that provides information other than system statistics, objects (tables and indexes, and so on), such as a running environment, additional, more accurate statistics, to help the optimizer choose a more appropriate execution plan for the SQL sta

The SQL Server execution plan teaches me how to create indexes? I am not very familiar with the index, so the test results are of no value, or even some people are misleading. I am sorry here, but where did I fall. Application scenarios Or use the Product table as an example. The table structure is as follows: There is such a business scenario: to obtain a list

The SQL parsing and execution plan generation of Impala is implemented by impala-frontend (Java), and the listening port is 21000. The user submits a request through the Beeswax interface BeeswaxService. query (). The processing logic at the impalad end is determined by voidImpalaServer:

Label:This document is based on the relevant data collated, summarized, mainly on the Oracle database, to obtain the most authoritative and correct method of SQL statement execution plan, and also explained in detail the meaning of the options available in each method and how to use, so as to facilitate everyone and their daily work to consult the use of Because

Clear data and execution plan cache: DBCC DROPCLEANBUFFERSDBCC FREEPROCCACHE Open statistics: SET STATISTICS IO ON SET STATISTICS TIME ON Open the execution plan: SETSHOWPLAN_TEXT ONSETSHOWPLAN_ALL ONSETSTATISTICS PROFILE ONSETSHOWPLAN_XML ONSETSTATISTICS PROFILE XML Differences between options C

Label: After a piece of SQL code is written, you can initially predict the performance of the SQL at run time by looking at the SQL execution plan, especially if you find that the SQL statement is inefficient, we can

Php:It is usually the beginning of the code you want to check to record a time, the end of the record a time. Take the difference value,the efficiency of database SQLSQL explain (MySQL), enable slow query log to record slow queries. Usually also depends on the database design is reasonable, the demand is reasonable and so on.But this time is generally very fast, in less than a second, so you can not directly use mktime ()function Getmicrotime () {Lis

parameterized SQL is to allow different parameters of the query reuse execution plan, but unfortunately, when the data distribution is uneven, reuse of the execution plan has caused the database damage, in the case of the normal

reading the query plan, includingMsdnsome articles in the library. We are not going to expand or replace them here. In fact, we will provide many of these links at this level/Reference. Displays the graphical execution plan (http://msdn.microsoft.com/zh-cn/library/ms178071.aspx) is a good start. Other useful resources

oracle| Statement | The autotrace that executes Sqlplus is a very simple and convenient tool for analyzing SQL's execution plan, execution efficiency, and, in most cases, a very useful tool. 1. How to set up and use Autotrace Sql> Connect/as SYSDBA Sql> @?/rdbms/admin/ut

Sys.dm_exec_cached_plansYou see two adhoc (instant query), the join query I executed in the first step and the select I executed in step two.3. Now that we've got 2 adhoc plan_handle, what's the difference between using Dm_exec_sql_text to see their SQL?4. After reading the text cache, let's continue to look at the

use the index to return fields from the select list without having to read the data file again according to the index An index that contains all the data that satisfies the needs of the query is called the Overwrite index.Using where: means that the MySQL server is "filtered" after the storage Engine is recorded (Post-filter), and if the query fails to use the index, the role of

语句，执行时甚至不用访问表或索引Possible_keysIndicates which index MySQL can use to find rows in the table, and if there are indexes on the fields involved in the query, the index will be listed but not necessarily used by the query.KeyDisplays the index that MySQL actually uses in the query, and displays NULL if no index is used. If an overwrite index is used in the query, the

How to know the execution efficiency of a SQL statement, only know the following 3 kinds:1. Analysis of disk activity volume (IO) information through SQL statement execution:set STATISTICS io on (ON)/ set STATISTICS io off (off)2. The time consumed by parsing, compiling, and executing the SQL statement when it is exec

Tags: style blog http color os using AR strong SP1. each execution of the SQL statement generates an execution plan and is cached because the execution plan is generated with time overh

returns the data. In the case of this SQL statement, the efficiency difference is not very large. You can look at the I/O statistics: Table Scan: 　　 Clustered Index Scan: 　　 This is beyond the scope of this article, the efficiency is not in the context of this article, this article only consider the differences between the various scans, and why the resulting.3. Clustered Index LookupClustered Index Lookup: Scans a specific range of rows in a cluster

This article describes in detail how to optimize SQL Server database queries. There are many reasons for slow query speed in SQL Server databases. The following are common causes: 1. No index or no index is used (this is the most common problem of slow query and is a defec

-consuming or long-28ms. You do not have to pay attention to count (*) can use COUNT (1) or count (primary key), this discussion online is also a lot, I myself switch three kinds of writing also have no essential difference.At this point, we add the previously deleted nonclustered index back, and then look at the query plan and time:You can see the query

Create a test table Connect with user Jyu, create test table sql> conn Jyu/jyu; Connected.sql> CREATE TABLE T (ID number, name VARCHAR2 (100)); Table created. sql> INSERT INTO T select Rownum,object_name from dba_objects;47391 rows created. Sql> commit; Commit complete. To create an index sql>. t_idx1 on t (ID), i