Category：MySql
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Time：2019-10-24
preface For security, the root user of mysql only logs in the machine and does not authorize access to the external network. In this case, the mysql database can be connected through SSH tunnel. The following are the basic steps to configure a Mysql SSH tunnel connection. Without further ado, let’s take a look at […]
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Time：2019-10-23
1. Precompile mechanism (execute multiple times at one time to prevent SQL injection) 2. Precompile mechanism
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Time：2019-10-23
In the database table, we sometimes save a lot of duplicate data, the duplicate data waste resources, we want to delete it, what should we do? Let’s see. Let’s take a look at our table. Some of the data is repetitive. To find duplicate data, we can use the having statement in mysql, as shown […]
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Time：2019-10-21
Preface MySQL’s Master-Slave replication relationship is not strictly called “synchronization” or “master-slave synchronization”. In fact, in the early days, the master and slave of MySQL did not realize true “sync”, but “async”. MySQL master-slave replication can have multiple modes, the most classic and the earliest asynchronous replication. From version 5.5, there has been semi synchronous […]
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Time：2019-10-20
First, under Linux, check MySQL related directories ViewmysqlInstallation path for Execute querySQL mysql>show variables like ‘%dir%’; datadirData path Determine the running path and execute the command of importing and exporting MySQL databaseI. use mysqldump command to export database(Note: first CD to MySQL running path, and then execute the following command):1. Export data and table structure:Mysqldump […]
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Time：2019-10-20
Introduction As usual, let’s start with a scene~ Interviewer: “do you know the four characteristics of business?”You: “you know, acid, atomicity, consistency, isolation, durability!” “Interviewer: “you use MySQL database. Can you tell us how to implement these four features in InnoDB? “You: “I only know how isolation works, Balabala ~ ~”Interviewer: “let’s go back and […]
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Time：2019-10-19
Preface The reason why I wrote this article is from the previous post about SQL statement optimization, which explicitly mentioned that * should not be used to query in SQL statements, as the following rules say 2. Avoid using select * as much as possible. Returning useless fields will reduce query efficiency. As follows: SELECT […]
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Time：2019-10-19
The example of this paper describes the simple operation of adding, deleting, modifying and querying MySQL statement. To share with you for your reference, as follows: 1. Create a DB shop database. If the database does not exist, create it. create database if not exists db_shop; 2. Delete the database. If the data exists, delete […]
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Time：2019-10-18
Reprinted and excerpted from https://dev.mysql.com/doc/refman/8.0/en/innodb-doublewrite-buffer.html The doublewrite buffer is a storage area located in the system tablespace where InnoDB writes pages that are flushed from the InnoDB buffer pool, before the pages are written to their proper positions in the data file. Only after flushing and writing pages to the doublewrite buffer, does InnoDB write pages to their proper positions. […]
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Time：2019-10-18
Like code, you can annotate tables and columns in tables so that others know what they do. For some fields, after a certain period of time, the creator may not be able to recall its specific meaning, so annotation is particularly important. Adding notesComments are added by adding the comment keyword at the end of […]
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Time：2019-10-17
1.Redo Log The redo log is a disk-based data structure used during crash recovery to correct data written by incomplete transactions. During normal operations, the redo log encodes requests to change table data that result from SQL statements or low-level API calls. Modifications that did not finish updating the data files before an unexpected shutdown […]
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Time：2019-10-17
When MySQL performs DDL operations such as alter table, sometimes there is a waiting for table metadata lock scenario. In addition, once the operation of alter table tableA stops in the state of waiting for table metadata lock, any subsequent operation (including reading) of tableA cannot be performed, because they will also enter the waiting […]
