explain gigabytes

Mysql optimization practice (explain Index) and mysql practiceLab environment: 1. SQL tool: Navicat2 and SQL database. Use openstack database as an example. I. mysql index Query Show index from instances Result field explanation: Table: database Table name Non_unique: the index value is 0 if it cannot contain duplicate words. Yes, it is 1. Key_name: name of the index.The column serial number in the index, startin

The syntax for explain is as follows: Explain [extended] select ... from ... where ... If you use extended, you can use the show warnings statement to query the appropriate optimization information after you finish executing the explain statement. For example, we execute the Select UID from user where uname= ' Scofield ' ORDER by UID execution results will hav

Explain shows how MySQL uses indexes to process SELECT statements and join tables. Can help select better indexes and write more optimized query statements. Simply put, its role is to analyze query performance.The Explain keyword is very simple to use, just put it in front of the SELECT query statement.MySQL to see if the index is used, simply look at the type types. If it is all, then the query statement i

Tags: style blog http color io os using AR strongLet's take a look at the table structure of Arena_match_index, and notice the index structure of the table.CREATE TABLE ' Arena_match_index ' (' Tid ' int (ten) unsigned not NULL DEFAULT ' 0 ',' Mid ' int (ten) unsigned not NULL DEFAULT ' 0 ',' Group ' int (ten) unsigned not NULL DEFAULT ' 0 ',' Round ' tinyint (3) unsigned not NULL DEFAULT ' 0 ',' Day ' date is not NULL DEFAULT ' 0000-00-00 ',' BeginTime ' datetime not NULL DEFAULT ' 0000-00-00 0

Label:Explain select a.* from test A, (SELECT ID from test where level_id Because the deferred association returns the primary key of the desired data row by overwriting the index, then the primary key is associated with the original table to obtain the required data, so the speed is much faster than before. Overwrite the index (the query only accesses the index, that is, the query only needs to access the index, without having to access the data row, the simplest understanding, such as open a

Preface This article is translated from The wife of the author (Shubho), Farhana, plans to become a new software engineer (she was born and gave up later ), so the author tried to help her learn object-oriented design (OOD) based on her experience in software development and design ). Since the author started software development, the author often noticed that no matter how complicated the technical questions appear, it would be easier to explain fro

This article is translated from codeproject.ArticleRanking 3rd in the top articles, I think it is very good after reading it. I will translate it for the reference of students who do not want to read English. The wife of the author (Shubho), Farhana, plans to become a new software engineer (she was born and gave up later ), so the author tried to help her learn object-oriented design (OOD) based on her experience in software development and design ). Since the author started software developme

username from test1;insert into test1 (username) select username from test1;insert into test1 (username) select username from test1;insert into test1 (username) select username from test1;insert into test1 (username) select username from test1;insert into test1 (username) select username from test1;insert into test1 (username) select username from test1;insert into test1 (username) select username from test1;insert into test1 (username) select username from test1;insert into test1 (username) se

Tags: onclick Other date result XPL Union store key value GESIn MySQL, we can obtain information about how MySQL executes the SELECT statement through the EXPLAIN command, including the order in which the table joins and joins during the SELECT statement execution.Each column of the results of the EXPLAIN command is described separately below: Select_type: Represents the type of select, and the common v

How can we easily explain the following application examples of closures and closures in a specific project? In php, does {code...} play a similar role as below? {Code...} is generally used under what circumstances in a specific project? Can you give a small example of how to explain the following closure and closure application examples in a specific project? Php, function demo(){ $a=10; $b=20; $

You can add the explain statement before the select statement:Example: explain select * from test1Description of the EXPLAIN column:Table: displays the data of this row about which tableType: this is an important column that shows the type used by the connection. The connection types from the best to the worst are const, eq_reg, ref, range, indexhe, and ALL.Possi

When explain can be misleadingSee: http://www.mysqlperformanceblog.com/2006/11/12/when-explain-can-be-misleading/ (1) explain when estimating the number of rows, limit is not taken into account, so it is possible to estimate too many check rows for the query. (2) similar to select... full table scan queries such as from TBL limit n will be reported as slow qu

Based on PHP, I would like to explain some anti-fake tickets and php explanations. Based on PHP, I would like to explain some anti-ticket farming skills. php has always been a problem and cannot be fundamentally prevented. However, we can try to reduce the number of ticket refresh attacks. based on PHP, we will explain some anti-ticket refresh techniques and php

Now let's talk about the meaning of each parameter in the Oracle execution plan. The following is an example. Here is a supplement.: Trace types: Serial number Command Explanation 1 SET AUTOTRACE OFF This is the default value, that is, disable Autotrace. 2 SET AUTOTRACE ON EXPLAIN Show only execution plans 3 SET AUTOTRACE ON STATISTICS Only statistics of execution are displayed. 4

There are many ways to view execution plans. I will introduce them one by one in my blog in the future. This article describes the first method. You can use the explain plan command to view the execution plan.1. log on to the database with an hr user[Oracle @ ENMOEDU ~] $ Sqlplus hr/oracle @ ENMOEDUSQL * Plus: Release 11.2.0.3.0 Production on Thu Apr 10 00:11:00 2014Copyright (c) 1982,201 1, Oracle. All rights reserved.Connected:Oracle Database 11g En

The previous article introduced how to explain the struct and array in Oracle, Explain plan Select * from table (dept_array (department_type ( 1, -- DNO number (10 ), 'Name', -- name varchar2 (50 ), 'Location' -- location varchar2 (50) ) T Join Table2 T2 on T. DNO = t2.dno; Select * from table (dbms_xplan.display ); The running result contains the following data: Plan_table_output 1 plan hash v

Mysql> explain extended select count (*) from xuehao;+ ---- + ------------- + ------- + ------ + --------------- + ------ + --------- + ------ + ---------- + -------------------------------- +| ID | select_type | table | type | possible_keys | key | key_len | ref | rows | filtered | extra |+ ---- + ------------- + ------- + ------ + --------------- + ------ + --------- + ------ + ---------- + -------------------------------- +| 1 | simple | null | sel

What I saw on a website is well written and shared with you! I want to explain to my new employee what is work! At that time, the company recruited a large number of new students who graduated from undergraduate and postgraduate courses. The average age is 25 years. The new assistant is a girl I personally recruited after many interviews. Graduated from a prestigious university with a smart and lively personality. In private, I have to admit that

Original: https://mp.weixin.qq.com/s?__biz=MjM5NzAzMTY4NQ==mid=400738936idx=1sn= 2910b4119b9943bafdcfe950dc89e028scene=0uin=mjk1odmyntyymg%3d%3dkey= 04dce534b3b035ef3da41c55e69b6792390d87f8207be3e924d28fab0b6ac41a02549bf7410a7849c9f2e872273023e9 Devicetype=imac+macbookpro11%2c4+osx+osx+10.11.1+build (15B42) version=11020201lang=zh_cnpass_ Ticket=%2fjwu7qjjuvdwcla0zj%2bdltxfo8dewz247cbaqxufnyatmk8uev%2b76dkdlt2ljundGuide What are the key messages worth noting in explain's results? M

Please explain the process of recursion in detail. function Al_merge ($arrA, $arrB) { $arrC = array(); while(count($arrA)count($arrB)){ $arrC[]=$arrA['0'] Reply content: Please explain the process of recursion in detail.function Al_merge ($arrA, $arrB) { $arrC = array(); while(count($arrA)count($arrB)){ $arrC[]=$arrA['0'] Alas, you downvote the big real also not too impati