Programming VIP

1, Connection query Classification according to the way of table connection: Internal connection: equivalent connection, non equivalent connection and self connection External connection: left external connection (left connection), right external connection (right connection) Syntax: join ... on ... select ... from Table name 1 join Table na ...

1. DQL operation sheet 1.1 create database and copy tables Create a new db2 database CREATE DATABASE db2 CHARACTER SET utf8; Copy the emp table in the db1 database to the current db2 database 1.2 sorting The sorting effect of the query can only be displayed through the order clause, and the sorting effect will not be displayed thro ...

If you already know the basic commands, you can This link View specific usage Redis    Redis is the abbreviation of remote dictionary service, that is, remote dictionary service;    Redis is an in memory database (data is stored in memory, and the main data in mysql is stored in disk), KV database (key value), and data str ...

catalogue 1, MySQL PRIMARY KEY Set primary key constraint when creating table Set federated primary key when creating table Delete and modify primary key constraints II. MySQL FOREIGN KEY constraint and UNIQUE constraint Set foreign key constraints and unique constraints when creating tables 3, MySQL CHECK constraint (CHECK) Delete ch ...

Introduction to Exception and the use of transactions 1, Java exceptions: Error and Exception 1. Overview of exception mechanism The exception mechanism refers to how the program handles when an error occurs in the program. Specifically, the exception mechanism provides a safe channel for the program to exit. When an error occurs, the proces ...

Common statements: --show database SHOW DATABASES; #Create a table score in stuinfo, including column id,name, and grade scores --Select database USE stuinfo; --Create table CREATE TABLE score(    id INT,    -- auto_increment Automatic growth    NAME VARCHAR(20),-- varchar() Variable length string    grade INT); #Query table Syntax: sele ...

preface In our daily APP or website, we often need to access data. For example, in wechat, we need to store a series of information such as our user name, mobile phone number, user password, etc. Relying on the Java related knowledge learned before can no longer meet this demand. Now the most basic and widely used application program is relati ...

On the idea of login registration business and the realization of some codes Recently, I started the development of mobile terminal project. As I am in the background, I certainly can't avoid realizing the functions that every app should have: login and registration. At the beginning, I felt very confused. So I write a blog here to share with ...

1, Definition of HIVE Hive is a data warehouse tool based on Hadoop, which can map structured data files into a data table, and can read, write and manage data files in a way similar to SQL. This Hive SQL is abbreviated as HQL. Hive's execution engines can be MR, Spark and Tez. essence The essence of Hive is to convert HQL into MapReduce task ...

previously on The previous section explained how to use oauth2 in the front end, how to modify user status and write authentication logic to adapt to oauth2This section will explain how to make a simple background management page What is the background management page? The essence of background management is CRUD of database recordsIt is us ...