ANSI SQL语法
好不容易才有点时间来复习下数据库里最基本的SQL语法：
SQL Data Manipulation Language (DML)
SQL (Structured Query Language) is a syntax for executing queries. But the SQL language also includes a syntax to update, insert, and delete records.
These query and update commands together form the Data Manipulation Language (DML) part of SQL:
- SELECT - extracts data from a database table
- UPDATE - updates data in a database table
- DELETE - deletes data from a database table
- INSERT INTO - inserts new data into a database table
SQL Data Definition Language (DDL)
The Data Definition Language (DDL) part of SQL permits database tables to be created or deleted. We can also define indexes (keys), specify links between tables, and impose constraints between database tables.
The most important DDL statements in SQL are:
- CREATE TABLE - creates a new database table
- ALTER TABLE - alters (changes) a database table
- DROP TABLE - deletes a database table
- CREATE INDEX - creates an index (search key)
- DROP INDEX - deletes an index
