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📚 preface What is SQL? Official explanation: SQL (Structured Query Language) is used to manage relational database management system (RDBMS). What can SQL be used for? Generally speaking, it allows you to access and process the database, including data insertion, query, update and deletion. SQL is almost a necessary skill for ...

#Advanced 6: link query /* Meaning: it is also called multi table query. When the query fields come from multiple tables, the join query will be used Cartesian product phenomenon: Table 1 has m rows, table 2 has n rows, and the result is mn rows Cause: there is no valid continuous condition How to avoid: adding valid connection conditions Class ...

Time attribute Flink supports three time concepts related to stream data processing: Processing Time, Event Time and Ingestion Time. Blink SQL only supports two time types: Event Time and Processing Time: Event Time: Event Time (usually the most original creation time of data). Event Time must be the data provided in the data store.Process ...

12. Dynamic SQL What is dynamic SQL? Dynamic SQL is to generate different SQL statements according to different conditions Dynamic SQL is one of the powerful features of MyBatis. If you have used JDBC or other similar frameworks, you should be able to understand how painful it is to splice SQL statements according to different conditions. Fo ...

SQL statement execution order  I think this article is very good. Why can't the sub table order by? The following description gives me a further understanding of SQL. Reading catalog preparation SQL logical query statement execution order #Execute FROM statement #Perform ON filtering #Add external row #Perform WHERE filtering #Execute GROUP ...

catalogue 1. Principle Secondary injection process 2. Experimental process (1) View initial users table (2) Registered user (3) Modify user password 3. Cause   Specific code 4. Defensive measures 1. Principle Secondary injection can be understood as the injection caused by the malicious data constructed by the attacker being st ...

Firstly, the mybatis framework encapsulates sql statements and executes them through tag and attribute parsing in the form of xml. We know that the sql statements inserted into the table are: INSERT INTO table name (column 1, column 2,...) VALUES (value 1, value 2,...) During the insertion process, the database will add transactions by d ...

The implementation here is based on MySQL 8. catalogue 1. Meaning and understanding of window function 2. Syntax of window function 2.1 understanding of window name syntax 2.2 understanding of sorting statements in Windows 2.3 understanding of window subset 2.4 window function 1. Meaning and understanding of window function Window fun ...

The following contents are for reference only. If there are errors, please correct them. Design requirements Realize the management of student information, classes, departments and majors; Realize the management of course and student achievement information; Realize the information management of students' rewards and punishments; Create ...

Problem Description: a deadlock problem suddenly occurs during the peak period of online projects! When the user operation gets stuck, the deadlock is thrown directly in the background Viewing the log, it is found that deadlock loserdataaccessexception (Deadlock found when trying to get lock; try restarting transaction...) occurs when updating ...