SQL-DDL (operations on libraries and tables)

DDL operation database

CRUD (addition, deletion, modification and check)

C (Create)-create a database

1. Create a database

CREATE DATABASE 数据库名;

Found that the database db1has been created

2. Determine whether the database already exists, create a database if it does not exist

CREATE DATABASE IF NOT EXISTS 数据库名;

First, we use the first method to create another db1database.

An error occurs Can't create database 'db1'; database exists,
and then use the second method to create it.

Finally, use the second method to create it.db2

3. Create a database and specify the character set

CREATE DATABASE 数据库名 CHARACTER SET 字符集;

Specify the character set encoding to gbkcreatedb3

R (Retrieve)-View the database

1. View all databases

SHOW DATABASES;

2. View the creation information of a specified database

SHOW CREATE DATABASES 指定数据库名称;

U (Update)-modify the name of the database, character set

ALTER DATABASE 数据库名 DEFAULT CHARACTER SET 字符集;

The modified db3character set is determined by gbk->utf-8

D (Delete)-delete the database

1. Delete the database

DROP DATABASE 数据库名;

2. Determine whether the database already exists, delete the database if it exists

DROP DATABASE IF EXISTS 数据库名;

The deletion process is the same as above

Use && to switch database

1. View the database in use

SELECT DATABASE(); 

2. Use/Switch Database

USE 数据库名;

DDL operation table

C (Create)-create a table

CREATE TABLE 表名 (
字段名 1 字段类型 1,
字段名 2 字段类型 2
);

Create a table student in the db1 database to

display the information in the student table

R (Retrieve)-query table

1. Query a table in a database

SHOW TABLES;

Query db1

query mysql

2. Query table structure

DESC 表名;

Query proc table

Query host table

D (Delete)-delete table

First copy the same table stu with student

1. Delete the table

DROP TABLE 表名;

2. Determine whether the table already exists, delete the table if it exists

DROP TABLE IF EXISTS 表名;

U (Update)-modify the table

1. Modify the table name

ALTER TABLE 表名 RENAME TO 新表名;

Rename the table student to stu

2. Modify the character set of the table

ALTER TABLE 表名 character set 字符集;

3. Add a column

ALTER TABLE 表名 ADD 列名 类型;

Add a column of gender in stu

4. Modify the name and type of the column

ALTER TABLE 表名 CHANGE 旧列名 新列名 类型;

Modify the gender name and type in the stu table

5. Only modify the column type

ALTER TABLE 表名 MODIFY 列名 新的类型;