Account management of MySQL

Catalog

One 、SQL sketch

1.SQL Overview

2.SQL The advantages of  

Two 、 Three paradigms of database  

3、 ... and 、 Account management

  Four 、SQL Basic statement

        5、 ... and 、 Case study

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One 、SQL sketch

1.SQL Overview

Structure Query Language( Structured query language ) abbreviation SQL, It was approved by the National Bureau of standards (ANSI) American Standard for relational database language , Later by international standards organization (ISO) International standards adopted as relational database language . The database management system can be through SQL Management database ; Definition and operation data , Maintain data integrity and security .

2.SQL The advantages of  

1、 Easy to learn , It has strong operability
2、 Most important database management systems support SQL
3、 Highly unprocessed ; use SQL When operating a database, most of the work is done by DBMS Done automatically
 

Two 、 Three paradigms of database  

1、 First normal form (1NF) It means that each column of the database table is an inseparable basic data line ; in other words ： The value of each column is atomic , It's indivisible .
2、 Second normal form (2NF) It's in the first paradigm (1NF) On the basis of , Satisfying the second paradigm (2NF) We must first satisfy the first paradigm (1NF). If the table is a single master key , Then columns other than the primary key must be completely dependent on the primary key ; If the table is a composite primary key , Then columns other than the primary key must be completely dependent on the primary key , You can't rely on just a part of the primary key .
3、 Third normal form (3NF) It is based on the second paradigm , That is, to meet the third paradigm, we must first meet the second paradigm . Third normal form (3NF) requirement ： The non primary key column in the table must be directly related to the primary key, not indirectly ; in other words ： Non primary key columns cannot depend on each other .
 

3、 ... and 、 Account management

Access to the company's database is divided , If one day you become a manager or .... So authorization or something can't be arranged .

# Create user ---- Zhang San 
CREATE user zs;

# View user information 
select host,user,authentication_string from user;

# Set the password 
ALTER USER 'zs'@'%' IDENTIFIED WITH mysql_native_password BY '123456';

# Give permission to the user 
grant all on studentmanager.* to 'zs'@'%'
# Take back authority 
revoke delete on studentmanager.* from 'zs'@'%'
# View all permissions 
show grants for 'zs'@'%'

create user ls;

ALTER USER 'ls'@'%' IDENTIFIED WITH mysql_native_password BY '123456';

grant select,delete on studentmanager.tb_class to 'ls'@'%'

CREATE DATABASE zhw

# Query database version 
select version()

# Query the database 
show databases;

  Four 、SQL Basic statement

        Build table

CREATE TABLE book(
id INT,# Number 
bName VARCHAR(20),# Book name 
price DOUBLE,# Price 
authorId INT,# Author No 
publishDate DATETIME# Publication date )

        The modification of table

#① Change column names 
ALTER TABLE book CHANGE COLUMN publishdate pubDate DATETIME;
​
#② Modify the type or constraint of the column 
ALTER TABLE book MODIFY COLUMN pubdate TIMESTAMP;
​
#③ Add new column 
ALTER TABLE author ADD COLUMN annual DOUBLE;
​
#④ Delete column 
ALTER TABLE book_author DROP COLUMN annual;
​
#⑤ Modify the name of the table 
ALTER TABLE author RENAME TO book_author;
​
DESC book;

        Table delete

DROP TABLE IF EXISTS book_author;
SHOW TABLES;

        Table replication

#1. Just copy the structure of the table 
CREATE TABLE copy LIKE author;
​
#2. Copy the structure of the table + data 
CREATE TABLE copy2
SELECT * FROM author;
​
# Copy only part of the data 
CREATE TABLE copy3
SELECT id,au_name
FROM author
WHERE nation=' China ';
​
​
# Just copy some fields 
CREATE TABLE copy4
SELECT id,au_name
FROM author
WHERE 0;

        5、 ... and 、 Case study

 

 1、 Every purchase in January is full 20 Total consumption of yuan

select sum(order_amt) from t_user where user_id=(select distinct user_id from t_user where user_id not in (select user_id from t_user where  order_amt < 20 or not MONTH(ORDER_TIME) = 1))

2、 People who only ordered spicy hot and hamburgers in January