MySQL multi table query (implemented by SQL joins)
catalogue
multi-table query
multi-table query
introduce: SELECT..... FROM... WHERE...AND/OR/NOT ORDER BY...(ASC/DESC) LIMIT...
Which city does the employee named 'Abel' work in?
SELECT *
FROM employees
WHERE last_name='Abel';
SELECT *
FROM departments
WHERE department_id=80;
SELECT *
FROM locations
WHERE location_id=2500;
2. How to ...
Posted on Sat, 20 Nov 2021 12:47:54 -0500 by waskelton4
MySQL scheduled backup database
1, The mysqldump command backs up data
MySQL provides a convenient tool mysqldump for exporting database data and files from the command line. We can export database contents directly from the command line.
#MySQL dump common
mysqldump -u root -p --databases Database 1 database 2 > xxx.sql
2, mysqldump common operation examples
1. Back ...
Posted on Sat, 20 Nov 2021 11:47:53 -0500 by lottos
What's new in. NET6 -- struct optimization
Some optimizations have been made for Struct in. NET6. Let's take a look at the optimizations for Struct in. NET6 through some cases.
1, Record Struct
Although there was a record in the previous version, the record in the previous version is a class and a reference type, but the record struct is a value type and a structure. Its usage is as f ...
Posted on Sat, 20 Nov 2021 10:03:29 -0500 by royalsolo
Day455. Basic SELECT statement & operator mysql
Basic SELECT statement
1, SQL overview
1. SQL background
In 1974, IBM researchers published a paper "sequence: a structured English query language", which unveiled database technology. Up to now, this structured query language has not changed much. Compared with other languages, the half-life of SQL can be said to be very long. S ...
Posted on Sat, 20 Nov 2021 09:34:12 -0500 by Arrow
Database Experiment 2
Experiment 2: create and manage database
Experimental content
1. Create database Assume that the SQL Server service has been started and log in to the computer as Administrator (the file name is customized); Please use the Management interface mode and T-SQL statement respectively to realize the following operations:
It is required to create ...
Posted on Sat, 20 Nov 2021 07:02:17 -0500 by The Swedish Tower
❤️ Liver explosion for 3 days! 20000 word graphic SQL zero basic entry, not afraid you can't learn, just afraid you don't collect! ❤️
📚 preface
SQL language has a history of more than 40 years. Since it was applied, it has been almost everywhere. Every payment record we consume, every user information we collect and every message we send will be stored in the database or its related products, and the language to manipulate the database is SQL! SQL is almost a necessar ...
Posted on Sat, 20 Nov 2021 06:42:25 -0500 by phpBever
Distributed Chapter 7 FastDFS
Chapter 1 Introduction to FastDFS
FastDFS overall architecture
Two institutions: client (usually our program) + server (tracker [scheduling] + storage node [file storage and management])
Chapter 2 Establishment of FastDFS environment
Start tracker, storage and upload files
fdfs_trackerd /etc/fdfs/tracker.conf
fdfs_storaged /etc/fdf ...
Posted on Sat, 20 Nov 2021 04:35:17 -0500 by yjanni
MySQL master-slave replication
1, Introduction to master-slave replication
1.1 what is master-slave replication
Copy the binlog log of the master server to the slave server for execution to achieve the consistent state of the master-slave data, which is called master-slave replication. In a word, what the master database does is what the slave database does.
1.2 why s ...
Posted on Fri, 19 Nov 2021 18:28:24 -0500 by ravira
Android room tells about object relationship through the story of big head son
Pay attention to official account and learn more knowledge
summary
sqlite is a relational database, so object relationship is an important part. For example, the data we define includes forests and trees, and forests contain trees. At this time, the defined forest should contain a tree object, which is the object relationship between forest ...
Posted on Fri, 19 Nov 2021 15:34:49 -0500 by mkosmosports
Grouping and filtering of DQL statements
Note: the following will use the emp table in the mysql database in the mysql database management system as an example
This content continues from the previous study notes: DQL statement 2 in SQL (learning note 3)
1, Grouping function
Grouping function is also called multi line processing function, and there are only 5 multi line proce ...
Posted on Fri, 19 Nov 2021 13:32:06 -0500 by nainil