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database Basic concepts of database It is more convenient to manage the data in developmentPreviously, data was managed through IO flow Use the character stream to read one line of data at a timeEncapsulate the read data as an objectAdd multiple objects to the collectionTraverse the collection to determine whether the object is the object ...

1. mysql master image configuration   first, we need to obtain the dockerfile file from the docker hub official website for subsequent modifications. The address is as follows:   https://github.com/docker-library/mysql.git    then copy one copy of the 8.0 folder and name the other 8.0_slave. Enter the 8.0 folder, where ther ...

1. De duplication query According to the database tables and data created before, we put forward a demand to query the student numbers of all students who took the exam select `studentno` from `result` --Query the student numbers of all students with grades According to the results, we can see that there are a lot of duplicates in the dat ...

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 ...

1, What is shiro Apache Shiro is a powerful and easy-to-use Java security framework that performs authentication, authorization, password, and session management. With Shiro's easy to understand API, you can get any application quickly and easily, from the smallest mobile application to the largest network and enterprise application. Develop ...

Operation database Operation database Several basic database operation commands: update user set password=password('123456')where user='root'; Change Password flush privileges; Refresh database show databases; Show all databases use dbname；Open a database show tables; show database mysql All tables in describe user; Display table mysql ...

Database MySql Basics 1. Function classification? What functions are often used? lower upper substr length Trim (remove the leading and trailing spaces and do not remove the spaces in the middle) str_to_date(%Y-%m-%d) date_format Format (decimal) round Random number ifnull (if empty, replace with 0) Aggregate function / grouping function Grou ...

Pre observation tips The database of this query exercise comes from the Internet, you can baidu yourself!!!! database SET FOREIGN_KEY_CHECKS=0; -- ---------------------------- -- Table structure for dept -- ---------------------------- DROP TABLE IF EXISTS `dept`; CREATE TABLE `dept` ( `DEPTNO` int(11) NOT NULL COMMENT 'Department number' ...

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 ...

Database file https://download.csdn.net/download/yougcave/18897401 Database screenshot emp employee form dept Department salgrade wage scale   1. Name of the person who gets the highest salary in each department The first step is to find out the maximum salary of each department select deptno, max(sal) maxsal from emp group by de ...