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introduction:This paper prefers practice rather than methodology. The writing method of SpringBoot unit test mentioned in this paper is not an official solution, but a writing method that the author thinks is more convenient and efficient. Each team and even each developer in the team may have their own writing habits and styles. As long as the ...

Optimization of a query You should encounter this scenario. A self incrementing primary key is set in MySQL, but some data is subsequently deleted, resulting in discontinuous primary keys. You can use the following command to query those discontinuous primary keys. -- Writing method 1 select id from (select id from Table name order by id asc ...

Note: this blog is MySql table operation instruction 1. If you want to learn the basic MySql instructions, you can use the author Blog Learning; If you want to practice further, you can do it after learning Operation 2 After that, according to Blog MySql instance Practice! Add, delete, query and modify ~ simple instructions Create table ...

This article is mainly aimed at the addition, deletion, modification and query of MySQL and upgrading again. If you want to see the basic additions, deletions and changes, you can see the previous article of the blogger. Here, the blogger posts a link for you: https://blog.csdn.net/weixin_53033446/article/details/119005596?spm=1001.2014.3001.55 ...

preface This semester, we have a course of database principle and application, which is very difficult at the beginning, mainly because we didn't clarify the relationship between mathematical logic and database syntax in the process of SQL learning. Today, I would like to summarize my learning about SQL. I only briefly introduce the implem ...

PRIMARY KEY constraint Primary key is used to uniquely identify each record in a table. You can define one or more columns as primary keys. There can only be one primary key on a table;It is not recommended to update the primary key;No two rows on the primary key column have the same value (i.e. duplicate value), and NULL (NULL) is not allowed ...

What are constraints? In order to ensure the integrity (accuracy and correctness) of the data in the table, some restrictions are added to the table. It is a basic rule of table design in database. Using constraints can make data more accurate and reduce redundant data (dirty data). Database integrity constraints are divided into the followin ...

Welcome to the MySQL technical articles shared by the great SQL community. If you have any questions or want to learn, you can leave a message in the comment area below. After seeing it, you will answer itProblem descriptionThe problem comes from a group friend. In short, he uses mysqlbinlog tool to read binlog for recovery, but finds that the ...

backgroundThe timing scenario of the Internet of things is one of the hottest directions at present. Massive time series data such as vehicle trajectory data, vehicle status monitoring data and sensor real-time monitoring data need to be stored in the database. In general, the following requirements exist in such scenariosData high write, low r ...

4. DQL query data (the most important) 4.1 DQL (date query language: Data Query Language) All query operations use it, selectSimple queries and complex queries are availableThe core language and the most important statement in the databaseMost frequently used statements select[ALL | DISTINCT] { * | TABLE.* | [table.field1[as alias1][,table. ...