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What do you know MySQL Storage engine , Talk about their characteristics briefly
- Innodb 5.5 The default storage engine used after version , Storing data is more secure
- blackhole The black hole will disappear when it is stored
- memory Memory storage , The data disappears after exiting
- MyIsam 5.5 The default storage engine before version , The stored data is called Innodb faster
Complete syntax and considerations for creating tables
create table indicate ( Field name Field type （） constraint condition );
MySQL What are the basic data types
Integer type
floating-point
Character
enumeration , aggregate

Yesterday's review

Storage engine

"""
 There should be different processing mechanisms for different data 

 see MySQL All storage engines 
show engines;

Innodb
	MySQL5.5 The default storage engine after version 
	 Support transactions   Row lock   Foreign keys      Data is more secure 
	 Creating a table generates two files 
		 Table structure file 
		 Table data file 
MyIsam
	MySQL5.5 The default storage engine before version 
	 Although it has no data security Innodb reliable   But the query speed is faster Innodb faster 
	 Creating a table generates three files 
		 Table structure file 
		 Table data file 
		 Table index file 
memory
	 Memory engine 
	 Temporary data storage  
	 Creating a table will generate a file 
		 Table structure file 
blackhole
	 Black holes 
	 Creating a table will generate a file 
		 Table structure file 
"""

Complete syntax for creating tables

#  grammar 
create table  Table name (
	 Field name 1  Field type ( Width )  constraint condition ,
     Field name 2  Field type ( Width )  constraint condition ,
     Field name 3  Field type ( Width )  constraint condition 
)
#  Be careful 
1  Field names cannot be repeated in the same table 
2  Width and constraints are optional   Field name and field type are required 
3  The last field cannot be followed by a comma 


#  In general, the width is the limit on the storage data 
#  Constraints can have multiple   Is an additional limitation

Strict mode

#  When using a database   Try to make the database work less ！！！

show variables like '%mode';

set session
set global sql_mode = 'STRICT_TRANS_TABLES';

Basic data type

"""
 integer 
	TINYINT INT BIGINT
	 The default is signed 
	
	int(4)
	 The numbers in integer brackets are not used to restrict storage 
	 If there are less than four digits, fill them with spaces by default 
	 Enough for four, how many to save  
	
	zerofill
	
	 summary   When defining integer fields in the future   In fact, you don't need to add your own width 
	 Because integers have their own width   It's enough to show all the numbers 
	
	
 floating-point 
	float(255,30)
	double(255,30)
	decimal(65,30)
	 As long as it's floating point   There are two numbers after the brackets 
		 The first number represents the total number of digits 
		 The second digit represents the decimal place 
	
	 accuracy 
	float < double < decimal
	
	 Expand : In fact, in actual production   A lot of data that seems to need to be stored in integer or floating-point type 
	 Internal may be stored in character type 
	
 Character type 
	char(4)   Fixed length 
		 Only a maximum of four characters can be stored   Beyond error reporting   Do not exceed the default to complete with blank space 
	varchar(4)   Lengthening 
		 Only a maximum of four characters can be stored   Beyond error reporting   Not more than a few save a few 
	
	char Vs varchar
	char
		 Waste space 
		 Access convenient   Simple violence   Directly access according to the fixed number of bits 
	
	varchar
		 Save a space 
		 But compared to char  Its access speed is slow 
			 Because it needs a when accessing data   Headlines 
	
	 Previously used char quite a lot   Limit varchar quite a lot 
	
 Time type 
	date   Specific date 
	datetime   Mm / DD / yyyy HHM / S 
	time   Minutes and seconds 
	year   year ( Limited scope )

 Enumeration and collection type 
	 enumeration enum
		 A commonplace   
	 aggregate set
		 More than a multiple-choice ( You can also single select )
	gender enum('male','female','others')
	hobby set('read','sangna','DBJ','hecha')
	 Your data can only be sourced from the options provided by the field   You can't make it up 
"""

constraint condition

"""
zerofill
unsigned
not null
"""

Summary of today's content

constraint condition
Create relationships between tables ( constraint )( a key )
Modify the complete syntax of the table
Copy table
Assignment ( How to judge table relationships and how to establish table relationships )

Today's content is detailed

constraint condition

default The default value is

#  Supplementary information    When inserting data, you can specify fields 
create table t1(
	id int,
    name char(16)
);
insert into t1(name,id) values('jason',1);

create table t2(
	id int,
    name char(16),
    gender enum('male','female','others') default 'male'
);
insert into t2(id,name) values(1,'jason');
insert into t2 values(2,'egon','female');

unique only

#  It's unique 
create table t3(
	id int unique,
    name char(16)
);
insert into t3 values(1,'jason'),(1,'egon');# Report errors 
insert into t3 values(1,'jason'),(2,'egon');
# Joint only 
"""
ip and port Represents the unique address of the host 
 A single can be repeated , But loading together must be unique 
"""
create table t4(
id int,
ip char(16),
port int,
unique(ip,port)
);
insert into t4 values(1,'127.0.0.1',8080);
insert into t4 values(2,'127.0.0.1',8081);
insert into t4 values(3,'127.0.0.2',8080);
insert into t4 values(4,'127.0.0.1',8080);   Report errors

primary key Primary key

"""
1. In terms of constraint effects alone primary key Equivalent to not null + unique
 Non empty and unique ！！！
"""
create table t5(id int primary key);
insert into t5 values(null);   Report errors 
insert into t5 values(1),(1);   Report errors 
insert into t5 values(1),(2); 
"""
2. In addition to its binding effect   It's still Innodb Storage engine organizes data based on 
Innodb When creating tables, the storage engine must have primary key
 Because it's like a catalog of books   It can help prompt query efficiency and is also the basis for creating tables 
"""
# 1  There is only one primary key in a table   If you don't set the primary key   You will search from top to bottom until you encounter a non empty and unique field, which will be automatically upgraded to a primary key 
create table t6(
	id int,
    name char(16),
    age int not null unique,
    addr char(32) not null unique
);

# 2  If there is no primary key or any other non empty and unique field in the table   that Innodb A hidden field provided internally will be used as the primary key , Hiding means you can't use it   The query speed cannot be prompted 

# 3  A table should usually have a primary key field   And usually will id/uid/sid Field as primary key 
#  Single field primary key 
create table t5(
    id int primary key
	name char(16)
);
#  Combined the primary key ( Multiple fields are combined as the primary key of the table   In essence, it is also a primary key )
create table t7(
    ip char(16),
    port int,
    primary key(ip,port)
);

"""
 Also means that   In the future, when we create tables id The field must be added primary key
"""

auto_increment Self increasing

#  When there are too many numbers   It is too troublesome to maintain artificially 
create table t8(
	id int primary key auto_increment,
    name char(16)
);
insert into t8(name) values('jason'),('egon'),('kevin');

#  Be careful auto_increment It is usually added to the primary key   You cannot add... To a normal field 
create table t9(
	id int primary key auto_increment,
    name char(16),
    cid int auto_increment
);
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key

Conclusion

"""
In the future, you can create a table id( Unique identification of the data id、uid、sid) Field time
id int primary key auto_increment
"""

Add

delete from t1 After deleting the data in the table The self increment of the primary key will not stop

truncate t1 Clear the table data and reset the primary key

The relationship between tables

"""
 Define an employee table   There are many fields in the table 
id name gender dep_name dep_desc
"""
# 1  The organizational structure of the table is not very clear ( Can be ignored )
# 2  Waste hard disk space ( Can be ignored )
# 3  The scalability of the data is very poor ( Something that cannot be ignored )

#  How to optimize ？
""" The above problem is similar to that you write all the code in one py In file """
 Split employee table    Employee table and department table

Foreign keys

"""
Foreign keys are used to help us establish the relationship between tables
foreign key
"""

Table relations

"""
There are at most four relationships between tables
   One-to-many relation
       stay MySQL There is no more one-to-one talk in the relationship
       One to many For one more It's called one to many ！！！
   Many to many relationship
   One to one relationship
   It doesn't matter.
"""

One-to-many relation

"""

 When judging the relationship between tables   Not familiar with the situation in the early stage   Be sure to follow my advice to you

 The perspective-taking    Consider from the perspective of two tables

 Take employee table and department table for example

     Stand on the employee list first

         Think about whether an employee can correspond to multiple departments ( Can one employee data correspond to multiple Department data )

             You can't ！！！

            ( It is impossible to draw a direct conclusion   Be sure to consider both tables completely )

     Then stand on the Department table

         Think about whether a department can correspond to multiple employees ( Can a department data correspond to multiple employee data )

             can ！！！

     Come to the conclusion

         The employee table and department represent one-way one to many

         So the table relationship is one to many

"""

foreign key

    1  One to many table relationship     Foreign key fields are built in  More sides

    2  When creating tables   It must be built first  Associated table

    3  When entering data   You must also enter  Associated table

# SQL Statement to establish a table relationship

create table dep(

    id int primary key auto_increment,

    dep_name char(16),

    dep_desc char(32)

);

create table emp(

    id int primary key auto_increment,

    name char(16),

    gender enum('male','female','others') default 'male',

    dep_id int,

    foreign key(dep_id) references dep(id)

);

insert into dep(dep_name,dep_desc) values('sb Teaching department ',' Teaching and educating '),(' The Ministry of Foreign Affairs ',' Multiparty diplomacy '),('nb Technology Department ',' Department with limited technical capacity ');

insert into emp(name,dep_id) values('jason',2),('egon',1),('tank',1),('kevin',3);

#  modify dep Inside the watch id Field

update dep set id=200 where id=2;   no way

#  Delete dep The data in the table

delete from dep;   no way

# 1  Delete the employee data corresponding to the teaching department first   Then delete the Department

     The operation is too cumbersome

# 2  Truly realize the relationship between data

     Updates are synchronized

     Delete synchronously

"""

 update cascade    >>>    Synchronize updates

 cascading deletion    >>>    Sync delete

"""

create table dep(

    id int primary key auto_increment,

    dep_name char(16),

    dep_desc char(32)

);

create table emp(

    id int primary key auto_increment,

    name char(16),

    gender enum('male','female','others') default 'male',

    dep_id int,

    foreign key(dep_id) references dep(id)

    on update cascade  #  Synchronize updates

    on delete cascade  #  Sync delete

);

insert into dep(dep_name,dep_desc) values('sb Teaching department ',' Teaching and educating '),(' The Ministry of Foreign Affairs ',' Multiparty diplomacy '),('nb Technology Department ',' Department with limited technical capacity ');

insert into emp(name,dep_id) values('jason',2),('egon',1),('tank',1),('kevin',3);

Many to many

"""
 Book list and author list 
"""
create table book(
	id int primary key auto_increment,
    title varchar(32),
    price int,
    author_id int,
    foreign key(author_id) references author(id) 
    on update cascade  #  Synchronize updates 
    on delete cascade  #  Sync delete 
);
create table author(
	id int primary key auto_increment,
    name varchar(32),
    age int,
    book_id int,
    foreign key(book_id) references book(id) 
    on update cascade  #  Synchronize updates 
    on delete cascade  #  Sync delete 
);
"""
 Create... As described above   Don't try to succeed at all ！！！
 In fact, we just want to record the relationship between books and authors 
 For many to many field table relationships   You cannot create foreign keys in two existing tables 
 I need you to open another one alone   It is specially used to store the relationship between the data of two tables 
"""
create table book(
	id int primary key auto_increment,
    title varchar(32),
    price int
);
create table author(
	id int primary key auto_increment,
    name varchar(32),
    age int
);
create table book2author(
	id int primary key auto_increment,
    author_id int,
    book_id int,
    foreign key(author_id) references author(id) 
    on update cascade  #  Synchronize updates 
    on delete cascade,  #  Sync delete 
    foreign key(book_id) references book(id) 
    on update cascade  #  Synchronize updates 
    on delete cascade  #  Sync delete 
);

One to many

"""
id name age addr phone hobby email........
 If a table has too many fields   Not all fields can be used in every query 
 Split the watch in two   
	 User table 
		 User table 
			id name age
		 User details table 
			id addr phone hobby email........
	
	 Standing user table 
		 Can a user correspond to multiple user details     You can't ！！！
	 Stand on the detail sheet 
		 Can a detail belong to multiple users        You can't ！！！
	 Conclusion : One way one to many doesn't hold   So the table relationship between the two at this time 
		 It's one-on-one 
		 Or it doesn't matter ( Good judgment )

 Customer form and student form 
	 Before you sign up, you are a client 
	 After signing up, the students ( During this period, some customers will not sign up )
"""

 one-on-one   Foreign key fields can be created on either side   But it is recommended that you build it in a table with high query frequency 
create table authordetail(
	id int primary key auto_increment,
    phone int,
    addr varchar(64)
);
create table author(
	id int primary key auto_increment,
    name varchar(32),
    age int,
    authordetail_id int unique,
    foreign key(authordetail_id) references authordetail(id) 
    on update cascade  #  Synchronize updates 
    on delete cascade  #  Sync delete

Modify table

# MySQL Case insensitive 
"""
1  Modify the name of the table 
	alter table  Table name  rename  The new name of the table ;

2  Add fields 
	alter table  Table name  add  Field name   Field type ( Width )   constraint condition ;
	alter table  Table name  add  Field name   Field type ( Width )   constraint condition  first;
	alter table  Table name  add  Field name   Field type ( Width )   constraint condition  after  Field name ;

3  Delete field 
	alter table  Table name  drop  Field name ;

4  Modify fields 
	alter table  Table name  modify  Field name   Field type ( Width )  constraint condition ;
	
	alter table  Table name  change  Old field name   new field name   Field type ( Width )  constraint condition ;
	
"""

Copy table

"""
 We sql The result of a statement query is actually a virtual table 
"""
create table  Table name  select * from  Old table ;   Cannot copy primary key   Foreign keys  ...

create table new_dep2 select * from dep where id>3;

Assignment

practice ：

Account information table , User group , Host table , Host group

# User table 
create table user(
id int not null unique auto_increment,
username varchar(20) not null,
password varchar(50) not null,
primary key(username,password)
);

# User group table 
create table usergroup(
id int primary key auto_increment,
groupname varchar(20) not null unique
);

# Host table 
create table host(
id int primary key auto_increment,
ip char(15) not null unique default '127.0.0.1'
);

# Line of business table 
create table business(
id int primary key auto_increment,
business varchar(20) not null unique
);

# Build relationship ：user And usergroup

create table user2usergroup(
id int not null unique auto_increment,
user_id int not null,
group_id int not null,
primary key(user_id,group_id),
foreign key(user_id) references user(id),
foreign key(group_id) references usergroup(id)
);

# Build relationship ：host And business
create table host2business(
id int not null unique auto_increment,
host_id int not null,
business_id int not null,
primary key(host_id,business_id),
foreign key(host_id) references host(id),
foreign key(business_id) references business(id)
);

# Build relationship ：user And host
create table user2host(
id int not null unique auto_increment,
user_id int not null,
host_id int not null,
primary key(user_id,host_id),
foreign key(user_id) references user(id),
foreign key(host_id) references host(id)
);

practice

#  Class table 
cid	caption
#  Student list 
sid sname gender class_id
#  The teacher table 
tid	tname
#  The curriculum 
cid	cname	teacher_id
#  League tables 
sid	student_id course_id number

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