MySQL basic database creation foundation

Create database

value type

The date type

String type

Spatial data types

# Create table 
# The way 1：
USE atguigudb;
SHOW CREATE DATABASE atguigudb;# By default UTF8
SHOW TABLES;
CREATE TABLE IF NOT EXISTS myemp1( # Users are required to have permission to create tables 
	id INT,
	emp_name VARCHAR(15),# Use VARCHAR To define a string , Its length must be indicated when it is used 
	hire_date DATE 
);
# View table structure 
DESC myemp1;
SHOW CREATE TABLE myemp1;

SELECT *FROM  myemp1;
# The way 2：  Based on existing tables 
CREATE TABLE myemp2
AS
SELECT employee_id,last_name,salary
FROM employees;
DESC myemp2;
DESC employees;
SELECT*FROM employees



CREATE TABLE myemp3
AS
SELECT e.employee_id,e.last_name,d.department_name
FROM employees e JOIN departments d
ON e.department_id = d.department_id

SELECT * FROM myemp3;

# Create a table employees_cpoy, Realize to employees Replication of tables , Include table data 
CREATE TABLE employees_cpoy
AS
SELECT *
FROM employees;
SELECT * FROM employees_cpoy

# Create a table employees_blank, Realize to employees Table replication , Excluding table data 

CREATE TABLE employees_blank
AS
SELECT *
FROM employees;
SELECT * FROM employees
WHERE department_id > 10000;
#where 1=2;# Mountain without edges , Tiantianhan , But I dare to fight with you .

Delete 、 modify the database

DESC myemp1;
## Modify table 
# Add a field  --->alter table
ALTER TABLE myemp1
ADD salary DOUBLE(10,2);#2 Decimal places   By default, it is added to the last field position in the table 

ALTER TABLE myemp1
ADD phone_number VARCHAR(20) FIRST; #

ALTER TABLE myemp1
ADD email VARCHAR(45) AFTER emp_name;# Insert ** after 

# Modify a field 
# Generally, the field type will not be modified 
ALTER TABLE myemp1
MODIFY emp_name VARCHAR(25);

ALTER TABLE myemp1
MODIFY emp_name VARCHAR(35) DEFAULT 'aaa';


# Rename field 
ALTER TABLE myemp1
CHANGE salary monthly_salary DOUBLE(10,2);

ALTER TABLE myemp1
CHANGE email my_email VARCHAR(50);
# Delete a field 
ALTER TABLE myemp1
DROP COLUMN my_email;
## rename table 
# The way 1
RENAME TABLE myemp1
TO myemp11;
SHOW TABLES;

# The way 2
ALTER TABLE myemp2
RENAME TO myemp12;

## Delete table 
DROP TABLE myemp12;
## Clear the table 
# Clear all the data in the table , But the table structure is preserved 
SELECT *FROM employees_cpoy;
TRUNCATE TABLE employees_cpoy;	
SELECT *FROM employees_cpoy;
DESC employees_cpoy;

#DCL  in  COMMIT  and  ROLLBACK
#COMMIT： Submit data , Once executed COMMIT, The data is permanently stored in the database , This means that rollback is not possible 
#ROLLBACK： Undo Data , Once executed ROLLBACK, Data rollback can be realized , Roll back to the last time COMMIT after .

# contrast  TURNCATE TABLE  and  DELECT FROM
# The same thing ： All data in the table can be deleted , At the same time, the table structure is preserved 
# Difference ：
# TRUNCATE： Clear table data , Once you do this , Clear all table data , At the same time, data cannot be rolled back 
# DELECT FROM ： Once you do this , All table data can be cleared （ No WHERE）. At the same time, the data can be rolled back 

/* DDL and DML Explanation  ①DDL Once the operation of is executed, it cannot be rolled back . Instructions SET autocommit = FLASE Yes DDL Operation failure （ Because it's executing  DDL It must be executed once after the operation COMMIT, And this COMMIT Not affected by instructions ） ②DML By default, the operation of cannot be rolled back . But if it's being carried out DML Before , Yes  SET autocommit = false. Then the operation can be rolled back , The default is true */
# demonstration  ： DELETE FROM
#1
COMMIT;# Submit data 
#2
SELECT* FROM myemp3
#3
SET autocommit = FALSE;
#4
DELETE FROM myemp3
#5
SELECT* FROM myemp3
#6
ROLLBACK;
#7
SELECT* FROM myemp3


# demonstration  ： TRUNCATE TABLE
#1
COMMIT;# Submit data 
#2
SELECT* FROM myemp3
#3
SET autocommit = FALSE;
#4
TRUNCATE TABLE  myemp3
#5
SELECT* FROM myemp3
#6
ROLLBACK;
#7
SELECT* FROM myemp3


############
#MySQL8.0 New characteristics ：DDL Atomization of 
# Do the following 
# If it is 5.0 Will delete book1, Report errors book2 non-existent 
# If it is 8.0 Will delete bokk1, Report a mistake later book2 And roll back book1 surface 
# Atomization ： Either all or none , Cannot separate , whole 
CREATE DATABASE mytest;
USE mytest;
CREATE TABLE book1(
book_id INT,
book_name VARCHAR(255)
);
DELETE TABLE book1,book2
SHOW TABLES;

Create management table exercise

practice 1

# Create and manage table exercises 
# Create database test01_office, Indicates that the character set is utf-8, And perform the following operations under this database 
CREATE DATABASE IF NOT EXISTS test01_office CHARACTER SET 'utf8';

USE test01_office;

# Create a table  dept01
/*  Field   type  id INT(7) NAME VARCHAR(25) */
CREATE TABLE dept01(
id INT(7),
`name` VARCHAR(25)
);

# Will table departments Insert the data in the new table dept02 in 
CREATE TABLE dept02
AS
SELECT * FROM atguigudb.`departments`

# establish emp01 surface 
/*  Field   type  id INT(7) first_name VARCHAR(25) last_name VARCHAR(25) dept_id INT(7) */
CREATE TABLE emp01(
id INT(7),
first_name VARCHAR(25),
last_name VARCHAR(25),
dept_id INT(7)
);
DESC emp01;
ALTER TABLE emp01
MODIFY last_name VARCHAR(50);

# according to employees establish emp2 surface 
CREATE TABLE emp02
AS 
SELECT*FROM  atguigudb.`employees`;

SHOW TABLES;
SHOW TABLES FROM test01_office;
# Delete emp01 surface 
DROP TABLE emp01;

# Will table emp02 Rename it to emp01
#alter table emp02 rename to emp01; 
RENAME TABLE emp02 TO emp01;

# In the table dept02 neutralization emp01 Add new column  test_column
ALTER TABLE emp01 ADD test_column VARCHAR(10)
ALTER TABLE dept02 ADD test_column VARCHAR(10)

# Delete the table directly emp01 Column in department_id
ALTER TABLE emp01
DROP COLUMN department_id;
DESC emp01;

practice 2

# Create database test02_market
CREATE DATABASE IF NOT EXISTS test02_market CHARACTER SET 'utf8';
# Open database 
USE test02_market;
SHOW CREATE DATABASE test02_market;
# Create data table  customers
CREATE TABLE IF NOT EXISTS customers(
	c_num INT,
	c_name VARCHAR(50),
	c_contact VARCHAR(50),
	c_city VARCHAR(50),
	c_birth DATE
);
SHOW TABLES;
DESC customers;

# take c_contact Move field to c_birth The back of the field 
ALTER TABLE customers
MODIFY c_contact VARCHAR(50) AFTER c_birth;
DESC customers;

# take c_name Change the data type to varchar(70)
ALTER TABLE customers
MODIFY c_name VARCHAR(70);

# take c_contact The field is renamed c_phone
ALTER TABLE customers
CHANGE c_contact c_phone VARCHAR(50);

# increase c_gender Fields to c_name Back , The data type is char(1)
ALTER TABLE customers
ADD c_gender CHAR(1) AFTER c_name;

# Change table name to customers_info
RENAME TABLE customers
TO customers_info;
DESC customers_info;

# Delete field c_city
ALTER TABLE customers_info
DROP COLUMN c_city;
DESC customers_info;

practice 3

# Create database test03_company
CREATE DATABASE IF NOT EXISTS test03_company CHARACTER SET 'utf8';
# Access to database 
USE test03_company;

# Create table office
CREATE TABLE IF NOT EXISTS office(
officeCode INT,
city VARCHAR(30),
address VARCHAR(50),
country VARCHAR(50),
postalCode VARCHAR(25)
);
SHOW TABLES;

# Create table employees
CREATE TABLE IF NOT EXISTS employees(
empNum INT,
lastName VARCHAR(50),
firstName VARCHAR(50),
mobile VARCHAR(25),
`code` INT,
jobTitle VARCHAR(50),
birth DATE,
note VARCHAR(255),
sex VARCHAR(5)
);

DESC employees;

# Will table employees Of mobile Modify the field to code The back of the field 
ALTER TABLE employees
# If the modified length is unreasonable, an error will be reported 
MODIFY mobile VARCHAR(25) AFTER `code`;
DESC employees;

# Will table employees Of birth The field is renamed birthday
ALTER TABLE employees
CHANGE birth birthday DATE;

# modify sex Field , The data type is char(1)
ALTER TABLE employees
MODIFY sex CHAR(1);

# Delete field note
ALTER TABLE employees
DROP COLUMN note;
DESC employees;

# Add field name favoriate_activity, The data type is varchar(100)
ALTER TABLE employees
ADD favoriate_activity VARCHAR(100);
DESC employees;

# Table name employees The name of is changed to employees_info
RENAME TABLE employees TO employees_info;
DESC employees_info;