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Two tables, T1 and T2, have only one field, id int. Insert 1000 records each, and run the following statement:ExplainSELECT t1.id,t2.id from T1 INNER joins T2 on T1.id=t2.idShown below:The explanations are as follows:With the help of explain, you

description of the OPTIMIZE in the manual:OPTIMIZE [LOCAL | No_write_to_binlog] TABLE tbl_name [, Tbl_name] ...If you have deleted a large part of the table, or if you have made many changes to a table with variable-length rows (a table with a

SQL FOR XML alternative notation (with tag and union all, simple and easy to understand)Test environment: SQL, R2, 2010, 2012, 2014, etc.Declare @agent table (agentid int, Fname varchar (5), SSN varchar (one)) insert into @agent Select 1, ' Vimal ',

With the help of explain, you know when to add an index to the table to use the index to find records and make the select run faster.If some problems arise due to improper use of the index, you can run analyze table to update the table's statistics,

Nginx Learning (2) hello world Program Hello wrold 1 program 2 implementation steps 2.1config 2.2 module code implementation 2.3 compile the configuration file 3. Compile the module into nginx 1 Purpose of this section This section uses nginx to

1 PackageJFrame;2 3 Importjava.awt.*;4 Importjavax.swing.*;5 Public classJPanel8extendsjframe{6 //menu bar, not participating in layout7 jmenubar MB;8 //node-level menus9Jmenu[] Menu = {NULL,NULL,NULL,NULL,NULL};Ten JMenu mn00; One

SQL Injection on a site of Shanda game may cause leakage of the IP addresses and mobile phone numbers of current database users Shanda game was injected again, and its permissions were not high enough to query its own tables. You can see the IP

Android entry notes-data storage-SQLite, unit test Why do we need to add three lightweight databases (SQLite) today? Because it is really light. Sqlite is a lightweight database specially prepared by unembedded devices. Although it is small, it has

OPTIMIZE TABLE is used to reclaim unused database space. When rows of data on a table are deleted, the disk space occupied is not immediately reclaimed, the space is reclaimed after the Optimize table command is used, and the rows of data on the

We discussed the database performance optimization on the other hand, that is, the use of database server built-in tools to analyze and optimize. ▲show Perform the following command to understand the running state of the server: MySQL >show status;

If you put the keyword explain,mysql in front of the SELECT statement, it explains how it handles the Select, providing an order about how tables are joined and joined.Each output row of the explain provides information about a table, and each row

COALESCE (expression_1, expression_2, ..., expression_n) refer to each parameter expression in turn, and then stop and return the value if it encounters a non-null value. If all of the expressions are NULL, a null value will eventually be returned.

Transferred from: http://www.blogjava.net/persister/archive/2008/10/27/236813.htmlWith the help of explain, you know when to add an index to the table to use the index to find records and make the select run faster.If some problems arise due to

Sometimes, when using MySQL, you may find that even though a table deletes a lot of data, the data and index files of this table are surprisingly small. This is because when MySQL deletes data (especially text and blobs), it leaves a lot of data

SQL FOR XML also has a way of writing (with tag and union all, simple and easy to understand)Test environment: SQL, R2, 2010, 2012, 2014, etc.Declare @agent table (agentid int, Fname varchar (5), SSN varchar (one)) insert into @agent Select 1, '

A plain statement select * from T1, t2 where t1.id = t2.id and t1.name = ' a '; Under what circumstances is this statement most efficient?Table Connection Categories:1. Nested loops connection (Nested loop join)2. Sort Merge Connection (merge sort

Excerpt articleSQL join is used to query data from these tables based on the relationship between the columns in two or more tables. Note that the number of data records after join is not necessarily a simple connection to the left or right table,

1. Join syntax Overview Join is used to associate fields in multiple tables. The syntax is as follows: ... FROM table1 INNER|LEFT|RIGHT JOIN table2 ON conditiona Table1: Left table; table2: Right table. JOIN is divided into the following three

Author: Shandong Information Security Group Black. Eagle It is estimated that you have read 《OracleOnce injected into the actual penetration of China Unicom, this article will be a shock, but I do not know whether readers and friends have ever

In the WIN32 SDK environment, how do you create common basic controls? We know that if we use MFC, simple drag and drop to complete the creation of most of the control, but since we are programming with the Windows SDK API, of course, from the root