Introduction to SQL

最新推荐文章于 2025-09-13 19:07:06 发布

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最新推荐文章于 2025-09-13 19:07:06 发布

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文章标签：数据库

原文链接：http://www.cnblogs.com/wangzw/archive/2006/04/07/369523.html

本文介绍了SQL语言的基本概念，包括数据操作语言（DML）和数据定义语言（DDL）。DML部分涵盖了SELECT、UPDATE、DELETE和INSERT INTO等命令的使用；DDL部分则详细说明了如何创建、修改和删除数据库表及索引。

1.What is SQL SQL is an ANSI (American National Standards Institute) standard computer language for accessing and manipulating database systems. SQL statements are used to retrieve and update data in a database. 2.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 3.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

转载于:https://www.cnblogs.com/wangzw/archive/2006/04/07/369523.html