Introduction to MySQL database Basics

Little knowledge :MySQL The database that comes with it

 information_schema: Not a real watch , It's a view There are no real physical files in this database

mysq: This is a MySQL Core database , A lot of core data , There are many table files stored inside

performance_schema: Meaning of performance , A database that does some operations to improve performance , There are also many tables

test: Empty database

If you are not familiar with the database, try not to touch it

1. Basic concepts of database :

1.1 database : Folder

1.2 surface : file

1.3  data ; data  

 1.4    3 Species notes
        * Single-line comments : -- The comment or # The comment (mysql specific ) 
        *1 Multiline comment : /* notes */

       2 SQL classification
  2.1) DDL( Operating the database , surface ): Data definition language
            Used to define database objects ： database , surface , Column, etc. . keyword ：create, drop,alter etc.

        2) DML( Add or delete data in the table ): Data operation language
       It is used to add, delete and modify the data in the database . keyword ：insert, delete, update etc.

        3) DQL( Query data in table ): Data query language
       Used to query the records of tables in the database ( data ). keyword ：select, where etc.

        4) DCL( to grant authorization ): Data control language ( understand )
       It is used to define the access rights and security level of the database , And create users . keyword ：GRANT, REVOKE etc.