View: MySQL provides view function from version 5.0.1. Virtual tables (used as ordinary tables) are dynamically generated when using views. Only sql logic is saved, and query results are not saved.
Multiple places use the same query resultsThe sql statements used in the query results are complex
Posted on Wed, 27 Oct 2021 20:02:58 -0400 by Mohit_Prog
The core object of MyBatis
SqlSessionFactory is a very important object in the Mybatis framework. It is a compiled memory image of a single database mapping relationship. Its main function is to create an instance of SqlSession.SqlSessionFactory object, which can be built through SqlSessionFactoryBuilder object.
The code is as follows: ...
Posted on Sun, 24 Oct 2021 00:48:14 -0400 by Jeller
1, Introduction to SQL language
SQL statements are used to maintain and manage the database, including data query, data update, access control, object management and other functions.
SQL language classification
DDL: data definition language, which is used to create database objects, such as libraries, tables, indexes, etc.DML ...
Posted on Fri, 22 Oct 2021 03:09:59 -0400 by Anidazen
SQL implements continuous login days and maximum login days
Title: calculate the number of consecutive login days of users Problem extension: users who log in for 3 consecutive days, maximum login days, etc
The field user id and login time date given in sheet1 are shown in the following table:
1. Cleaning data
Because it is the calculation ...
Posted on Thu, 21 Oct 2021 00:17:19 -0400 by PHP Newb
1. Create a database named text. Note that the ` ` symbol is the symbol below the Esc key in the upper left corner of the keyboard, not a comma. (if you use SQLyog to create a list, remember to refresh the list!!!)
Format: create database database name
CREATE DATABASE `text`
2. Create a table
CREATE TABLE IF NOT EXISTS `studen ...
Posted on Fri, 15 Oct 2021 16:35:26 -0400 by Hikari
Master various integrity definition methods of basic tables.Master the creation and use of users.Master the method of SQL statement for security control of database and table.
Use the graphical user interface to add the following constraints and indexes to the Student library, and verify the default ...
Posted on Fri, 15 Oct 2021 16:17:43 -0400 by prasad_deba
create index idx_seller_name_sta_addr on tb_seller(name,status,address);
1) . full value matching is the most efficient
explain select * from tb_seller where name='Xiaomi Tech ' and status='1' and address='Beijing'
2) . leftmost prefix rule If you index multiple columns, follow the leftmost prefix rule. This means that ...
Posted on Thu, 14 Oct 2021 18:36:04 -0400 by NeMoD
The 50 questions of SQL are widely circulated on the Internet. They are a classic and comprehensive set of questions. Recently, they have just joined the data development engineer, and SQL needs to be strengthened. Therefore, naturally, they can't miss this set of questions. Each question is written by themselves. If they can't, they have seen ...
Posted on Mon, 11 Oct 2021 23:07:51 -0400 by jl5501
This article mainly introduces 50 SQL query skills and query sentence examples. Taking student table, curriculum table, grade table and teacher table as examples, this paper explains the writing methods of SQL sentences under different needs. Friends in need can refer to it. It is suggested that comrades who often use MySQL collect them.
Posted on Mon, 11 Oct 2021 21:50:53 -0400 by keyurjbhatt