blocks|key|3261517|text|DDL+-更改架构。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3261518|这包括创建表、重命名列、删除视图等。这些语句是DDL的，尽管这些语句可能会创建(默认值)、alter+(按转换)，甚至丢失(删除的列)数据作为进程的一部分。基本上，任何CREATE/DROP/ALTER命令都是DDL。|offset|length|style|CODE|3261519|DML+-更改架构中的信息/数据；不更新模式。|3261520|这包括DELETE和UPDATE语句。|3261521|有时，必须同时使用DDL和DML来正确迁移模式；但它们是两类不同的SQL命令，DML从不导致模式更改。|3261522|entityMap^0|0|2C|H|0|0|3|6|A|6|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@$D|R|E|S|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|T|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|U|8|@$D|V|E|W|F|G]|$D|X|E|Y|F|G]]|9|@]|A|$]]|$1|L|3|M|5|6|7|Z|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|10|8|@]|9|@]|A|$]]]|O|$]]

DDL - alter the schema.

This including creating tables, renaming columns, dropping views, etc. Such statements are DDL even though such might create (default value), alter (by conversion), or even lose (removed column) data as part of the process. Basically, any <code>CREATE/DROP/ALTER</code> command is DDL.

DML - alter the information/data within the schema; without updating the schema.

This includes <code>DELETE</code> and <code>UPDATE</code> statements.

Sometimes DDL and DML must be used together to correctly migrate a schema; but they are two distinct categories of SQL commands, and DML never causes the schema to be changed.

blocks|key|467983|text|ALTER命令用于更改数据库的结构。这就是DDL所做的，即DDL语句用于定义数据库结构或模式。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|467984|而DML语句用于管理架构对象中的数据。|467985|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

ALTER command is used to alter the structure of the database. And this is what DDL does i.e., DDL statements are used to define the database structure or schema.

Whereas DML statement is used to manage data within schema objects.

blocks|key|3173973|text|原因是ALTER命令没有操作数据。它用于更改o列或表或其他DB对象的定义。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3173974|请参阅alter.asp|offset|length|3173975|entityMap|0|LINK|mutability|MUTABLE|url|http://www.w3schools.com/sql/sql_alter.asp^0|0|3|9|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

Cause ALTER command is not manipulating the data. It is used to change a definition of o column or table or other DB objects.

See 
<a href="http://www.w3schools.com/sql/sql_alter.asp" rel="nofollow">http://www.w3schools.com/sql/sql_alter.asp</a>

blocks|key|467999|text|“数据”是用户通过DDL定义的表中的数据。“元数据”是DBMS预定义的表中描述表(它们本身和用户定义的表)中的数据。因此，DML操作用户表中的数据，或者(通常只)从系统表中读取元数据，而DDL则定义(创建、更改、删除)用户表，并作为副作用更新系统表中的元数据。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|468000|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

The "data" is the data in the tables defined by the user via DDL. The "metadata" is the data in the tables pre-defined by the DBMS that describe the tables (themselves and those defined by the user). So DML manipulates data in user tables or (usually only) reads metadata from system tables while DDL defines (CREATEs, ALTERs, DROPs) user tables and as a side effect updates metadata in system tables.

blocks|key|468012|text|ALTER命令可以是DDL和DML。我知道过去是DDL，就像大多数对此作出回应的人一样。但是，使用MySQL+5.7.x，您将看到在用mysqld+--initialize+--console初始化数据库后不久，就会创建一个默认的根用户帐户及其相应的密码。您可以使用这个新创建的根用户帐户访问您的数据库，但是在登录后绝对没有什么可以做的。在此阶段允许的惟一SQL语句是ALTER语句。这用于更改初始化期间生成的默认密码。语法是ALTER+USER+'root'@'localhost'+IDENTITIED+BY+'new_password';。这是数据库唯一接受的语句。这将修改/更新/操作用户表中的数据(密码)。在这方面，我的结论是，ALTER语句可以是DDL和DML。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|468013|entityMap^0|1V|T|5X|1N|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

The ALTER command can be both DDL and DML. I have known ALTER to be DDL over the past just like the majority of those who have responded to this. However, with MySQL 5.7.x you will see that soon after initializing the database with <code>mysqld --initialize --console</code> a default root user account and its corresponding password is created. You can access your database with this newly created root user account BUT there is absolutely nothing that you can do after logging in. The only SQL statement allowed at this stage is the ALTER statement. This is used to change the default password generated during initialization. The syntax is <code>ALTER USER 'root'@'localhost' IDENTITIED BY 'new_password';</code> . This is the only statement that the database accepts. This modifies/updates/manipulates the data (password) in the users table. In this regard I have concluded that the ALTER statement can be both DDL and DML

I was going through the different commands in SQL and I came across alter command which is referred as DDL (Data Definition Language). We can alter the column and values in it, so we can manipulate the data with this command so why does alter command is not referred as DML (Data Manipulation Language).

I have googled and I can not come across some good explanation, so please help me with this.

Why alter command is referred as DDL and not DML?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋 

腾讯云代码助手

CODING DevOps

Cloud Studio

SDK中心

API中心

命令行工具

我正在使用SQL中的不同命令，我遇到了alter命令，它被称为DDL (数据定义语言)。我们可以修改列和它中的值，所以我们可以使用这个命令来操作数据，所以为什么alter命令不被称为DML (数据操作语言)。我已经在谷歌上搜索过了，我找不到一些好的解释，所以请帮我解决这个问题。

问为什么把alter命令称为DDL而不是DML？
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问为什么把alter命令称为DDL而不是DML？EN