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---------------------------------------------------------------Table building----------------Determine whether the student table exists declare num number; --Declare parameters num type number begin --start select count(1) into num from user_tables where table_name='student'; if num>0 then execute immediate 'drop table st ...

preface The text and pictures of this article are from the Internet, only for learning and communication, not for any commercial purpose. The copyright belongs to the original author. If you have any questions, please contact us in time for handling. Python has a lot of map visualization libraries. Although Matplotlib library is very power ...

1. After getting the user name, password and authentication code in the background: (1) Get the data submitted by the form (2) Determine whether the verification code is correct or not If the verification code is correct: 1. Encrypt the password in the form by MD5 MD5 moduleHttps://www.npmjs.com/package/md5 1,install cnpm install md5 --sav ...

JDBC fixing steps: Load driver String url="jdbc:mysql://localhost:3306/jdbcstudy?useUnicode=true&characterEncoding=utf-8&serverTimezone=GMT"; String username="root"; String password="123456"; Class.forName("com.mysql.cj.jdbc.Driver");//I don't know why com.mysql.jdbc.Driver will report an error. Please leave a message if you have any ...

preface In recent years, the business of leader 1-to-1 has been developing rapidly, but at the same time, he has encountered "growing pains". With the increasing number of microservices, the traffic further increases, and the hardware resources are a little overwhelmed. Then, how to achieve better flow protection measures such as curr ...

In the previous article, I introduced the logic of relationship mapping in Entity Framework Core. The foreign key mapping of EF left in the previous article is not mentioned, that is, the relationship of one-to-one, one to many, many to one, many to many, etc. This article will give you a detailed analysis of how to set up these mappings. 1. Re ...

1, Date and time functions 1. Function to get the current dateIt's the same. It's different CURDATE() : Used to get the current date of the system CURRENT_DATE() Used by the system to get the current date mysql> select CURDATE(),CURRENT_DATE(); 2. Get function of current time CURTIME() : Used to get the current time of the system mysql& ...

brief introduction The main application scenario of redis multiple data sources is to use multiple redis servers or multiple redis libraries. In this paper, the fastdep dependency integration framework is used to quickly integrate redis multiple data sources and integrate lettuce connection pool. Only after introducing dependency, configure th ...

check constraint means to filter one or more columns according to certain preset rules. If the condition is true, the filtering succeeds; if the condition is false, the filtering fails and the failure code is returned to the client. Why do you want to list and write this separately? You often encounter irregular SQL. In many cases, you can onl ...

Original address: https://mysqlserverteam.com/mysql-8-0-innodb-now-supports-instant-add-column/   For a long time, instant DDL has been one of the most popular InnoDB functions. For the growing and fast-growing data set, any network scale database must have the function of executing DDL immediately. Developers often need to add new columns to m ...