MySQL

The Tomcat and mysql i installed are all uncompressed versions. Installing and configuring Tomcat didn't cost me much time, mostly MySQL, and it almost cost me a day's time. Tomcat Installation Summary:First unzip the downloaded Tomcat package onto

Primary keyPrimary key: Primary key, which is used to uniquely constrain the data in this field, cannot be duplicated. There can be at most one primary key in a single table.Add primary KeyIn SQL, there are several ways to increase the primary key:

The MySQL Found_row () and Row_count () functions are used to calculate the number of rows affected by the previous statement, unlike the number of rows found_row used to get a select, and the number of rows Row_count used to get update or delete

1. Storage of MD5 in MySQL databaseStoring MD5 values with char (32) is a common technique. If your application uses varchar (32), it will cost an extra amount of unnecessary overhead for each string length that is worth it. This hexadecimal value

The book distinguishes itself from books such as the MySQL insider--innodb storage engine, which is mainly about indexing techniques in MySQL databases, and InnoDB, MyISAM, memory three storage engines. One of the main points of course is innodb.

# wget http://dev.mysql.com/get/mysql-community-release-el7-5.noarch.rpm# rpm -ivh mysql-community-release-el7-5.noarch.rpm# yum install mysql-community-serverRestart MySQL service after successful installation

In MySQL, how to complete the swap of 2 tables, such as T1 and T2 table name Swap, really just mutual rename so simple?Note that we want to complete 2 tables at the same time, otherwise it will cause data write failure, so we need to lock the table

/***** View User *****/Mysql> select User,host from Mysql.user;+------+-----------+| User | Host |+------+-----------+| Root | 127.0.0.1 || Root | :: 1 || Root | localhost |+------+-----------+3 rows in Set (0.01 sec)/***** Authorized User

Modify the MySQL installation directory under the My.ini file configuration:Add max_allowed_packet = 16M# MySQL Server Instance Configuration file#----------------------------------------------------------------------# Generated by the MySQL Server

Turn on slow log query for SQL configuration file, complete the following configuration and restart MySQLLog_queries_not_using_indexes#这个参数设置为ON, you can capture all SQL statements that do not use an index, although this SQL statement is likely

Type name Display length Database type Java type JDBC Type index (int) Describe VARCHAR L+n VARCHAR Java.lang.String 12 CHAR

#coding: Utf-8 ' @2016/04/13:to load raw-data.csv into db. Data is from CiteULike. " Import reimport mysql.connectordef Main (): # directory on Iiot ' s server infile = Open ('./raw-data.csv ', ' R ') Outfi Le = Open

These two days encountered a MySQL connection problem, find someone for a few days did not fix, first look at the error

Initial use of Ef6+mysqlThe project time can be long enough, custom development is the case. Customers really use the ability to basically no longer change. At first the project was implemented by PHP, and the desktop program was changed. With. NET

V. MySQL Backup recovery1. Backup method:Export the backup directly phpMyAdmin. We use root admin privileges to enter phpMyAdmin, and then export the MySQL database that needs to back up the website backup, recommended gzip compression format■

1. How can I see which storage engines are available for the server?To determine which storage engines your MySQL server can use, execute the following command:The code is as follows:Show engines;This command will take care of it.2. How do I choose

One1.1). Indexes reduce the amount of data the server has to examine.2). Indexes Help the server avoid sorting and temporary tables.3). Indexes turn random I/O into sequential I/O.Lahdenmaki and Leach ' s book also introduces a Three-star system for

MySQL database names are case-sensitive, depending on the file system, Windows does not differentiate, Linux differentiates. MySQL Database type integer type: TINYINT SMALLINT mediumint INT BIGINTNumber of bytes: 1 2 3 4 8modifier unsigned

Verify the Data Type in MySQL CHAR Char (M) M characters. The length is M * characters. The maximum length of M is 255. The verification is as follows: Mysql> create table t1 (name char (256) default charset = utf8; ERROR 1074 (42000): Column length

Verify the MySQL Data Type CHAR Char (M) M characters. The length is M * characters. The maximum length of M is 255. The verification is as follows: Mysql> create table t1 (name char (256) default charset = utf8; ERROR 1074 (42000): Column length