1) DDL (Data Definition Language) data definition language
a.create
创建表：create table tname(colName1 Datatype，coluName2 Datatype,……);
Description: This keyword can not only be used to create a table, but also can be used to operate, sequence (sequence), view (view), index (index)
b.alter
Modify the table structure:
- Add table fields: alter table tName add (colName Datatype);
- Delete table fields: alter table tName drop column colName;
- Modify the field name of the table: alter table tName rename oldName to newName;
- Modify the field type of the table: alter table tName modify colName Datatype;
c.truncate
Clear the data in the table but keep the table structure:
truncate table tName；
d.drop
Delete table structure:
drop table tName;
Description: This keyword can not only delete tables, but also delete indexes, sequences, views, stored procedures, functions, and triggers. The usage is similar .
2) DML (Data Manipulation Language): Data Manipulation Language
a.insert
Insert data: insert into tName(colName1, colName2,...) values(value1, value2,...)
Description: Insert data in all tables, tName (the fields in the table can be written later)
b.update
Modify data: update tName set colName1 = value, colName2 = value, ... where condition
c.delete
Delete data: delete from tName where Condition
description: when no conditions are added, delete all data in the table, the function is similar to truncate
3) DQL (Data Query Language): Data Query Language
select
Query data: select * from tName where condition
Description: query all data without writing conditions, * is a wildcard to indicate all fields, and you can also write specific field names in the table
4) TCL (Transaction Control Language): Transaction Control Language
a.commit: data submission
can be used directly
b.rollback: data rollbackcan be used directly
c.savepoint: save the restore pointcan be used directly
5) DCL (Data Control Language): Data Control Language
a.grant authorization operation
The right to create views for ordinary users: grant create view to username
b.revoke revoke permission
Revoke the user's right to create a view: revoke create view from username
c.create userCreate a user
create user username identified by password;
Description: The user name needs to be in English, and the password must be numbers or letters or English symbols or combinations