DDL语句

Posted 2021-02-12 linga

DDL语句主要是用来定义数据库，表，视图，索引，存储过程进行定义等，主要是定义数据库的结构。

DDL主要包括以下几个关键字：

• CREATE
• DROP
• ALter

CREATE

CREATE主要用于创建表和数据库，创建事务等，通常开发用于创建表。创建数据库的用法:

Name: 'CREATE DATABASE'
Description:
Syntax:
CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name
    [create_specification] ...

create_specification:
    [DEFAULT] CHARACTER SET [=] charset_name
  | [DEFAULT] COLLATE [=] collation_name

CREATE DATABASE creates a database with the given name. To use this
statement, you need the CREATE privilege for the database. CREATE
SCHEMA is a synonym for CREATE DATABASE.

创建表：

Name: 'CREATE TABLE'
Description:
Syntax:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    (create_definition,...)
    [table_options]
    [partition_options]

Or:

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    [(create_definition,...)]
    [table_options]
    [partition_options]
    select_statement

Or:

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    { LIKE old_tbl_name | (LIKE old_tbl_name) }

其他用法：

CREATE DATABASE
CREATE EVENT
CREATE FUNCTION
CREATE FUNCTION UDF
CREATE INDEX
CREATE PROCEDURE
CREATE SERVER
CREATE TABLE
CREATE TABLESPACE
CREATE TRIGGER
CREATE USER
CREATE VIEW
SHOW
SHOW CREATE DATABASE
SHOW CREATE EVENT
SHOW CREATE FUNCTION
SHOW CREATE PROCEDURE
SHOW CREATE TABLE

DROP

DROP主要用于删除表和数据库。删除数据库：

Name: 'DROP DATABASE'
Description:
Syntax:
DROP {DATABASE | SCHEMA} [IF EXISTS] db_name

删除表：

ame: 'DROP TABLE'
Description:
Syntax:
DROP [TEMPORARY] TABLE [IF EXISTS]
    tbl_name [, tbl_name] ...
    [RESTRICT | CASCADE]

其他用法：

DROP DATABASE
DROP EVENT
DROP FUNCTION
DROP FUNCTION UDF
DROP INDEX
DROP PROCEDURE
DROP SERVER
DROP TABLE
DROP TABLESPACE
DROP TRIGGER
DROP USER
DROP VIEW

ALter

用于修改数据库和表，修改数据库：

Name: 'ALTER DATABASE'
Description:
Syntax:
ALTER {DATABASE | SCHEMA} [db_name]
    alter_specification ...
ALTER {DATABASE | SCHEMA} db_name
    UPGRADE DATA DIRECTORY NAME

alter_specification:
    [DEFAULT] CHARACTER SET [=] charset_name
  | [DEFAULT] COLLATE [=] collation_name

修改表，修改的表是主键是，如果有自增列，需先修改掉自增，在修改主键：

Name: 'ALTER TABLE'
Description:
Syntax:
ALTER [ONLINE | OFFLINE] [IGNORE] TABLE tbl_name
    [alter_specification [, alter_specification] ...]
    [partition_options]

其他用法：

ALTER DATABASE
ALTER EVENT
ALTER FUNCTION
ALTER LOGFILE GROUP
ALTER PROCEDURE
ALTER SERVER
ALTER TABLE
ALTER TABLESPACE
ALTER VIEW

SQL分为以下几类：

1. DDL语句，数据库定义语句：数据库，表，试图，索引，存储过程进行定义。
2. DML语句，数据库操纵语句：出入数据INSERT，删除数据DELETE，更新数据UPDATE。
3. DCL语句，数据库控制语句：控制用户的访问权限GRANT，REVOKE。
4. DQL语句，数据库查询语句：查询数据SELECT。