11. MySQL View Learning Notes (Detailed)

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 ...

Posted by coolbeansdude51 on Sun, 10 May 2020 09:10:57 +0200

Slow log of MySQL Event scheduled tasks

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 ...

Posted by murp32 on Mon, 04 May 2020 13:43:41 +0200

java socket realizes the server, and the client has simple network communication. Chat

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 ...

Posted by Byron on Mon, 04 May 2020 03:09:22 +0200

Using rundeck scheduler to set up sending mail

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 ...

Posted by shivangp on Sun, 03 May 2020 23:51:10 +0200

Force sql to use an index

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 ...

Posted by daniel244rock on Sat, 02 May 2020 20:40:36 +0200

Index analysis of union primary key (Union index) in SQL Server (MySql)

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 ...

Posted by kathas on Fri, 01 May 2020 08:02:06 +0200

java learning notes

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 ...

Posted by nmreddy on Fri, 01 May 2020 07:44:47 +0200

Issue 03: column non empty and self increasing

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 ...

Posted by dayo on Wed, 29 Apr 2020 10:59:26 +0200

Case analysis: python operation database project

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 ...

Posted by andrewgk on Wed, 29 Apr 2020 08:50:53 +0200

hibernate -- HQL query summary

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 ...

Posted by JakeJ on Sun, 26 Apr 2020 16:09:42 +0200