Review summary of database

1. Operating the database

Database creation , Database selection , Delete database , View all databases , View the database in use

# Create database ( Default character set )
create database day01;
create database day01_0;
# Select database 
use day01;
use day01_0;
# View the database in use 
select database();
# Delete the specified database 
drop database day01_0;
# View all databases 
show databases;

2. Operation table

The creation of a table
Add fields in the table
Modify the properties in the field
Change the name of the field
Delete field
Show all the tables
The structure of the display table

# Create a student table 
create table t_stu(
stu_id int primary key auto_increment ,
stu_name varchar(20)  unique,
stu_gerder char(1) not null
);
# by t_stu Add a field to the table 
alter table t_stu add stu_grade varchar(20) not null;
# take t_stu surface stu_grade Change the field type to int
alter table t_stu modify stu_grade varchar(20);
# take t_stu surface stu_grade Change the field name to class
alter table t_stu change stu_grade class varchar(20) not null;
# take t_stu In the table class Field to delete 
alter table t_stu drop class;
# Show all the tables 
show tables;
# The structure of the display table 
desc t_stu;
# Delete table 
drop table t_stu;

3. Records in the operation table

preparation

create table product(
pid int primary key auto_increment,
pname varchar(40) ,
price double ,
num int
);

3.1 Additions and deletions

increase

insert into product values(null,' Apple computer ',18000.0,10);
insert into product values(null,' Huawei 5G mobile phone ',3000,20);
insert into product values(null,' Mi phones ',1800,30);
insert into product values(null,'iPhonex',8000,10);
insert into product values(null,'iPhone7',6000,200);
insert into product values(null,'iPhone6s',4000,1000);
insert into product values(null,'iPhone6',3500,100);
insert into product values(null,'iPhone5s',3000,100);
insert into product values(null,' instant noodles ',4.5,1000);
insert into product values(null,' coffee ',11,200); 
insert into product values(null,' Mineral water ',3,500);

modify

# Modify the operating 
# Set the price used to 8000
update product set price=800 ;
# Apple's price Set to 18000
update product set price=18000 where pname=' Apple computer ';
# Take Xiaomi's mobile phone price Set to 1800,num Set to 10
update product set price=1800,num=10 where pname=' Mi phones ';
# Bring down the price of Apple computers 1000
update product set price=price-20 where pname=' Apple computer ';

Delete

# Delete the records used 
delete from product01;
delete from product01 where pname=' Banana ';

3.2 Inquire about

Simple query

# Simple query 
# Query all data 
select * from product;
# Query specific columns （ Field ）
select pid, pname, price from product;
# Alias query 
select pname  The product name  ,price  Price  from product ;
# Go to check again distinct
select distinct price,num from product;
# Arithmetic query 
select price+180000  Price after change ,num from product;

Conditions of the query

# Conditions of the query where 
select * from product where price>800 or num>200;
select * from product where price>=800 and num=200;
# Fuzzy select * from product where pname like "iPh%";
# Range 
select * from product where pid not in(1,2,6,7);
select * from product where pid not between 2 and 5; Inquire about like

Sort query

# Environmental preparation 
#  Create student table ( Yes sid, The student's name , Student gender , Student age , Fractional column , among sid Auto grow for primary key )
CREATE TABLE student(
	sid INT PRIMARY KEY auto_increment,
	sname VARCHAR(40),
	sex VARCHAR(10),
	age INT,
    score DOUBLE
);

INSERT INTO student VALUES(null,'zs',' male ',18,98.5);
INSERT INTO student VALUES(null,'ls',' Woman ',18,96.5);
INSERT INTO student VALUES(null,'ww',' male ',15,50.5);
INSERT INTO student VALUES(null,'zl',' Woman ',20,98.5);
INSERT INTO student VALUES(null,'tq',' male ',18,60.5);
INSERT INTO student VALUES(null,'wb',' male ',38,98.5);
INSERT INTO student VALUES(null,' Xiao Li ',' male ',18,100);
INSERT INTO student VALUES(null,' Xiaohong ',' Woman ',28,28);
INSERT INTO student VALUES(null,' cockroach ',' male ',21,95);
select * from student;
# Sort query 
select * from student order by  score asc;

Aggregate functions

# Aggregate functions 
# Find out score minimum value 
select min(score) from student;
# Find out score Maximum 
select max(score) from student;
# Find out score The sum of the 
select sum(score) from student;
# Find the average 
select avg(score) from student;
# Calculate the number of records 
select count(*) from student;

Aggregate functions do not consider null