DDL language of MySQL database: create, modify alter, delete drop of databases and tables

MySQL Database DDL Language ： Creation of libraries and tables 、 modify 、 Delete

1、DDL Data definition language

• Library and table management

  • Library management ： establish 、 modify 、 Delete
  • The management of the table ： establish 、 modify 、 Delete

• The main keywords used

  • establish ：create
  • modify ：alter
  • Delete ：drop

• Be careful ： Delete here , Is to delete the entire table , The table will not exist after deletion ; and delete and truncate It refers to the operation of data , After deleting , Just the data was deleted , But the table still exists

2、 Library management

2.1 Library creation

CREATE DATABASE books;
CREATE DATABASE IF NOT EXISTS books;

2.2 Modification of the library （ Not much can be modified , Such as modifying the character set ）

ALTER DATABASE books CHARACTER SET gbk;

2.3 Deletion of Library

DROP DATABASE IF NOT EXISTS books;

3、 The management of the table

3.1 The creation of a table

• grammar ：

create table  Table name (
	 Name   The data type of the column [( length )  constraint ],
	 Name   The data type of the column [( length )  constraint ],
	....
	 Name   The data type of the column [( length )  constraint ]
);

• Case study 1： stay books Create tables in the database book

USE books;

CREATE TABLE book(
	id INT,
	bName VARCHAR(20),
	price DOUBLE,
	autherId INT,
	publishDate DATETIME
);

DESC book;

• Case study 2： Create table author

USE books;

CREATE TABLE author(
	id INT,
	auName VARCHAR(20),
	nation VARCHAR(20)
);

DESC author;

3.2 The modification of table

• Basic grammar ：

#① Change column names 
alter table  Table name  change column  The original name   New column names   The data type of the new column ;

#② Modify the length and constraint or data type of the column name 
alter table  Table name  modify column  Name   New data types ;

#③ Add new column 
alter table  Table name  add column  Name   Column type   constraint ;

#④ Delete column 
alter table  Table name  drop column  Name ;

#⑤ Modify the name of the table 
alter table  Table name  rename to  The new name of the table 

① Change the column name of the table

• Case study ： modify book Of publishDate by pubdate

ALTER TABLE book CHANGE COLUMN publishdate pubdate DATETIME;

② Modify the length and constraints of column names

• Case study ： modify pubdate The type of timestamp Time stamp

ALTER TABLE book MODIFY COLUMN pubdate TIMESTAMP;

③ Add new column

• Case study ： stay author Add an annual salary column to the table annual

ALTER TABLE author ADD COLUMN annual DOUBLE;

④ Delete column

• Case study ： Delete annual salary column annual

ALTER TABLE author DROP COLUMN annual;

⑤ Modify the name of the table

• Case study ： modify author Table name of

ALTER TABLE author RENAME TO book_author;

3.3 The deletion of the table

DROP TABLE book_author;
DROP TABLE IF EXISTS book_author; 


#  Displays the tables in the current database 
SHOW TABLES;

4、 A common way of writing （ Delete before creating ）

DROP DATABASE IF EXISTS  Library name ;
CREATE DATABASE  The name of the new library ;

DROP TABLE IF EXISTS  Table name ;
CREATE TABLE  The new name of the table (
...
);

5、 Replication of tables

5.1 Just copy the structure of the table Use like keyword

# preparation ： Create a table 
CREATE TABLE IF NOT EXISTS author(
	id INT,
	autherName VARCHAR(20),
    nation VARCHAR(20)
);
DESC author;
INSERT INTO author VALUES
(1,' Haruki Murakami ',' Japan '),
(2,' Mo yan ',' China '),
(3,' Yuhua ',' China ');

# Copy the structure of the table 
CREATE TABLE coptab LIKE author;

5.2 Copy table structure and data

CREATE TABLE coptab2 
SELECT * FROM author;

5.3 Copy only part of the data of the table

CREATE TABLE coptab3
SELECT id, autherName FROM author
WHERE nation = ' China ';

5.4 Copy only some fields of the table

CREATE TABLE coptab4
SELECT id, autherName FROM author
WHERE 0; # As long as the screening condition is not satisfied 

MySQL Learning notes — Silicon Valley