Mysql database (I)

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1. Database introduction

#  Database content :  A warehouse for storing data , Add, delete, modify and query the data in the database 
#  Data sheet : Where to store data 

2. Common databases

# Oracle: A large database of charges 
# mysql: Free open source   small 
# sqlserver: Charging medium-sized database 
# db2: Rechargeable 

3. Operating the database

#  The mouse operation  SQL Statement operation 
# SQL Code for :
# sql grammar :
#  Case insensitive 
#  Every sentence sql Semicolon after  a Inquire about  b Inquire about 

4. Data types commonly used in databases

# int type   The type of number 
# varchar(50)  character string   Indefinite length   byte 65535  male  2 Bytes 
# char  character string   Fixed length bytes  255 Bytes   male  2 Bytes   In the air 
# date date   Format 'yyyy-mm-dd'
# datetime date   Format 'yyyy-mm-dd hh:mm:ss'

5. Commonly used SQL operation

--  notes ctrl+/  add comments of explanations   Multiline comment /**/

--  use sql Statement create database   grammar : create database  Database name 
CREATE database ysly;

--  Delete database   grammar :drop database  Database name ;
drop database ysly;

--  new table 
--  grammar 
/* create table  Table name (  Field name   Field type   constraint condition ,  Field name   Field type , ...  Field name   Field type  )charset=utf8; */
-- not null  Primary key primary key  Self increasing  default

--  Set the primary key   The primary key cannot be empty , Auto increment must be a primary key 

--  Which data is the table you created in 
create table you.student1(
	id int PRIMARY key auto_increment,
	name varchar(20) default 'zz',
	age int,
	sex char(20)
	);
	
--  All fields in the table should be added  
--  The new data   Grammatical structure  insert into  Table name  values( Field name data , Field name data , Field name data , Field name data )
insert into you.student1 values(1,' Xiaocui ',18,' Woman ');
insert into you.student1 values(' Xiaocui 2',18,' Woman ');
--  Add only some fields 
-- insert into  Table name ( Field name , Field name , Field name )values( Field data , Field data , Field data )
insert into you.student1(name,age,sex) values(' Xiaocui 2',18,' Woman ');
insert into you.student1(age,sex) values(18,' Woman ');
--  Add multiple data at once  values value
-- insert into  Table name  values( Field name data , Field name data , Field name data , Field name data ),( Field name data , Field name data , Field name data , Field name data ),( Field name data , Field name data , Field name data , Field name data )
insert into you.student1(name,age,sex) value(' Xiaohong ',18,' Woman '),(' Xiaohong 2',18,' Woman '),(' Xiaohong 3',18,' Woman '),(' Xiaohong 3',18,' Woman ');
--  Query statement 
--  Inquire about  select * from  Table name ;
select * from you.student1;
--  Query partial data  select  Field name , Field name  from  Table name 
select id,name from you.student1;
--  Modify the statement  update  Table name  set  Field name  =  Revised content   The entire field of the entire table 
update you.student1 set name = ' Cui Hua ';
--  I don't want to modify the fields of the whole table   Just want to change the number to 1 Name   perhaps   Age is 18 Conditions  where  Conditional 
update you.student1 set name = ' Pickled cabbage resembling sauerkraut ' where id = 1;
update you.student1 set name = ' nori ' where age = 30;

--  Delete  delete from  Table name ;delete from  Table name  where Conditions ;
delete from you.student1 where id = 2;
delete from you.student1;

-- drop table  Table name ; Table structure 
drop table you.student1;

-- truncate table  Table name ;
truncate you.student;