Basic SQL DDL

Catalog

Database operation

Table operations - Inquire about

Table operations - establish

  data type

  modify

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Database operation

1. Inquire about

Query all databases

show databases;

Querying the current database

select database();

2. establish

create database [if not exists]  Database name  [default charset  Character set ] [collate  Sort rule ];

3. Delete

drop database [if exists] Database name ;

4. Use

use  Database name ;

Let's try

All databases are shown here

 

  Created a new one called lengxiang The database of , Show Query OK Then the creation is successful ！

like this , If there is already one named lengxiang The database of , If you create it again, you will report an error , Because it already exists .

 

Here is the execution of drop command , Deleted lengxiang This database .

 

use database , Then display the name of the current database .

Table operations - Inquire about

 1. Query all tables in the current database

show tables;

2. Query table structure

desc  Table name ;

3. Query the table creation statement of the specified table

show create table  Table name ;

Table operations - establish

create table  Table name (
        
         Field 1  Field 1 type [comment  Field 1  notes ],
         Field 2  Field 2 type [comment  Field 2  notes ],
         Field 3  Field 3 type [comment  Field 3  notes ],
        ………………
         Field n  Field n type [comment  Field n  notes ]
)[comment  Table annotation ];

Create a table

 

  data type

  modify

Add fields

alter table  Table name  add  Field name   type ( length ) [comment  notes ] [ constraint ];

Delete field

alter table  Table name  drop  Field name ;

Modify the name of the table

alter table  Table name  rename to  The new name of the table ;

Delete table

drop table [if exists]  Table name ;

Delete the specified table , And recreate the table

truncate table  Table name ;