sql creates tables, modifies table structures, and deletes tables

1. Create a database table

--Which database to use, if you don’t write this sentence, it is the default database, you can also use the mouse to select the current database

use testDB

--Create table

Create Table tablename

(

                                                                                                                                                                                           .

id int primary key not null identity(1,1),

--unique name varchar(20) not null unique

)

2. Delete table

Drop table table name

3. Modify the table structure

--Add column

Alter table table name

Add column name type

--Delete column

Alter table table name

drop cloumn column name

--Modify column, modify column Type

Alter table table name

Alter column column name type