MySQL learning record (1)

1.SQL Expression of stored data

SQL And EXCEL relative ：EXCEL----SQL

That's ok = Record

Column = Field

Intersection of row and column = Cell , To store data .

2.SQL Sentence classification

The meaning of the sentence is basically translation

2.1DDL（Data Definition Language, Data definition language ） It is used to create or delete the database used to store data and the tables in the database . Include ：

• CREATE ： Create objects such as databases and tables

• DROP ： Delete objects such as databases and tables

• ALTER ： Modify the structure of objects such as databases and tables

2.2DML（Data Manipulation Language, Data manipulation language ） Used to query or change records in a table . Include ：

• SELECT ： Query data in table

• INSERT ： Insert new data into the table

• UPDATE ： Update the data in the table

• DELETE ： Delete data from table

2.3DCL（Data Control Language, Data control language ） Used to confirm or cancel changes to data in a database . besides , You can also be right about RDBMS Whether or not the user has permission to operate the objects in the database （ Database table, etc ） To set . Include ：

• COMMIT ： Confirm changes to the data in the database

• ROLLBACK ： Cancel changes to the data in the database

• GRANT ： Give the user permission to operate

• REVOKE ： Cancel the user's operation permission

3.SQL Sentence writing rules

• SQL Statement to A semicolon （ ; ） ending

   Such as ：create database shop;
      show databases;

• SQL Case insensitive keywords , But the data inserted into the table is case sensitive
• win The system does not distinguish the case of table name and field name by default
• Constants are written in a fixed way
• Words need to be separated by half width spaces or line breaks , Do not use full width spaces as separators

I watched the tutorial from Alibaba cloud Tianchi  , For personal notes only .