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Added by GoncaloF on Fri, 11 Feb 2022 17:30:24 +0200
1, One to one mapping
Suppose that in the permission system, a user can only have one role, that is, the relationship between users and roles is limited to one-to-one relationship.
1.1 handling one-to-one relationships using automatic mapping
A user has a role. We add the role class SysRole field in the user class SysUser. As follows:
Added by djelica on Fri, 11 Feb 2022 09:45:56 +0200
1. Classification of sub query
1.1. Non associated subquery
Subquery statements can be executed separately without reference to any content in the included statement. It is called non associated subquery.
1.1.1. Single row single column subquery
The subquery statement returns a single row and single column table. This type of subque ...
JAVA program deployment
Operating environment: Galaxy Kirin + Feiteng CPU Project framework: Springboot + Mybatis + Dameng database jdk1 eight
The last one wrote the source code of the project, and this one mainly wrote the deployment of the project on the domestic operating system and the installation and creation of Dameng data ...
1, Explain tool introduction
Use the EXPLAIN keyword to simulate the optimizer to execute SQL statements and analyze the performance bottlenecks of your query statements or structures
Add the explain keyword before the select statement. MySQL will set a flag on the query. Executing the query will return the information of the execution plan i ...
Added by cyanblue on Wed, 09 Feb 2022 17:59:09 +0200
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⍨⃝ focus is not lost. Bloggers are still making efforts to prepare more wonderful content~ ☝ ʚʕ̯•͡˔•̯ ᷅ ʔɞ Xiao Joo is here to thank you for your support!
✨ 🅲🅼🅳 entry and exit 🅼🆈🆂🆀🅻
🌹 Connect to local database
mysql -uroot -p
. Exit mysql
Added by westen on Wed, 09 Feb 2022 12:54:03 +0200
The original content of GreatSQL community cannot be used without authorization. Please contact Xiaobian and indicate the source for reprint.[toc]This paper introduces how to use GreatSQL 8.0.25 to build a three node MGR cluster.1. Installation PreparationPrepare the following three servers:IPportrole172.16.16.103306mgr1172.16.16.113306mgr2172. ...
Added by sparrrow on Tue, 08 Feb 2022 19:10:28 +0200
🎈 Write in front
🙋♂️ Hello everyone, I'm super dream. You can call me Xiaomeng~
We all know that we have to deal with the database almost every day, whether in study or daily work. In order to better operate the database, our SQL knowledge reserve is essential. If you want to master SQL well, you must practice and stu ...
Added by Slippy on Tue, 08 Feb 2022 08:20:18 +0200
SQL knowledge points -- insert records
SQL knowledge points -- update records and delete records
Basic skills of SQL (I) -- SQL and database
Basic skills of SQL (II) -- basic query
Basic skills of SQL (III) -- aggregation and sorting
Advantages of view
scalar subquery ...
Single Line Processing Function
Data processing functions are also known as one-line processing functions
Features of one-line processing functions: one input corresponds to one output.
As opposed to single-line processing functions, multiline processing functions. (Multi-line processing function features: multiple inputs, corresponding to o ...
Added by edmore on Sun, 06 Feb 2022 19:17:52 +0200