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view Meaning: Understand as a virtual table and use it like a regular table A new feature of MySQL version 5.1 is data generated dynamically from tables For example: a comparison between a dance class and an ordinary class Differences between views and tables: Name Create Grammar Keyword Use Occupy physical space view ...

Preface Recently, we are trying to use a log system, graylog, to collect the slow query log of mysql for subsequent analysis, monitoring and alarm. The test steps have been completed and the logs have been collected successfully. During the test, you need to brush some slow query logs. In order to brush more logs and not have a greater impact o ...

There are some serious bug s in the code written before to realize simple network communication. Write in detail later. According to the last code, mainly increased the user registration, login page, and realized the real-time display of the current login status of the number of people. And solve some bug s not found last time. (refer to previo ...

1. Configure QQ mailbox to send mail 1.1 enable the SMTP service and obtain the authorization code 1.2 select account Start related services and generate authorization code 2. Enable sendmail service and postfile service [root@zydatahadoop001 rundeck]# service sendmail stop [root@zydatahadoop001 rundeck]# chkconfig sendmail off [r ...

SQL HINT (SQL HINT) is an important means to optimize the database, which is to add some hints in sql to optimize the effect. Let's learn about use index, ignore index, and force index; 1. Add use index after the query statement. You can suggest indexes to MySQL for reference, so that MySQL does not consider other indexes. explain select co ...

Recently, someone asked this question in the interview. Before that, they had not studied the specific use logic of the joint index, consulted several articles, and came to some conclusions after testing Test environment: SQL Server 2008 R2 The test results are similar to the query mechanism of MySql joint index. We can think that MySql is the ...

Getting to know JDBC 1, JDBC concept jdbc English full name: java database connectivity is a set of specifications for Java to access database, which can be understood as a set of classes and interfaces provided by java to connect database The relationship between jdbc and database driver: 　　 2, jdbc easy to use Usage process: (the driver jar ...

There are many attributes of fields in MySQL, and the impact on performance can be large or small, so it's necessary to explore the attributes. 1, NULL / NOT NULL For external programs, NULL is an unknown, imprecise, and indescribable value. Therefore, it is clearly stipulated in the development specifications of many companies that it must be ...

According to an example of a project, this paper records and shares the process and relevant settings of python's displaying the content of database to the program interface, and explores the usage of python's operating database. Main contents to be shared: 1. Displays the database contents. 2. Modify database content. 3. The table control spec ...

hibernate -- HQL query summary HQL overview: Simple query of HQL Alias query for HQL: HQL polymorphic query: Sort query for HQL: Paging query for HQL: HQL retrieves a single object: Condition query of HQL: HQL uses aggregate functions: HQL group statistics: Projection query of HQL: HQL ...