SQL classification and application

SQL Category:

　　Defined DDL: a definition of a database table, column, create alter drop

　　Operation DML: insert delete update ★ for updating the data table

　　Control DCL: for database access and security levels

　　Record DQL query table select from where ★

SQL syntax:

SQL is not case sensitive!

The most important SQL DDL statements:

　　CREATE DATABASE - create a new database

　　ALTER DATABASE - modify the database

　　CREATE TABLE - creates a new table

　　ALTER TABLE - change (change) database table

　　DROP TABLE - remove a table

　　CREATE INDEX - creates an index (search key)

　　DROP INDEX - deletes index