3、mysql学习之数据库定义语句

数据定义语句包括alter database、alter table、create database、create index、create table、drop database、drop index、drop table、rename table语法

 

一、ALTER DATABASE语法

常见的语法：

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

 

一般常用的话就是修改下数据库的字符集等

mysql> alter database test character set gbk;

 

二、ALTER TABLE语法

主要功能是修改表结构，或者是增加外键、主键等

ALTER [ONLINE|OFFLINE] [IGNORE] TABLE tbl_name

    [alter_specification [, alter_specification] ...]

    [partition_options]

 

mysql> alter table uuu add address varchar(30);

Query OK, 0 rows affected (0.09 sec)

Records: 0 Duplicates: 0 Warnings: 0

 

三、CREATE DATABASE语法

常见的用户就是创建数据库并且定义数据库编码及编码规则

 

CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name

    [create_specification] ...

 

create_specification:

    [DEFAULT] CHARACTER SET [=] charset_name

  | [DEFAULT] COLLATE [=] collation_name

 

四、CREATE INDEX语法

常见语法：

Syntax:

CREATE [ONLINE|OFFLINE] [UNIQUE|FULLTEXT|SPATIAL] INDEX index_name

    [index_type]

    ON tbl_name (index_col_name,...)

    [index_option]

    [algorithm_option | lock_option] ...

 

mysql> create index index_xiangys on student (dept(4) desc);

 

5、CREATE TABLE语法

常用语法

Syntax:

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name

    (create_definition,...)

    [table_options]

    [partition_options]

 

create_definition:

    col_name column_definition

  | [CONSTRAINT [symbol]] PRIMARY KEY [index_type] (index_col_name,...)

      [index_option] ...

 

create table test123(

id int(4) auto_increment,

uname char(4),

address char(40),

primary key (id)

);

 

六、DROP DATABASE语法

常用语法

Syntax:

DROP {DATABASE | SCHEMA} [IF EXISTS] db_name

 

七、DROP INDEX语法

常用语法：

Syntax:

DROP INDEX [ONLINE|OFFLINE] index_name ON tbl_name

    [algorithm_option | lock_option] ...

mysql> drop index index_xiangys on student;

 

八、DROP TABLE语法

常用语法：

DROP [TEMPORARY] TABLE [IF EXISTS]

    tbl_name [, tbl_name] ...

    [RESTRICT | CASCADE]

 

九、RENAME TABLE语法

常用语法：

Syntax:

RENAME TABLE tbl_name TO new_tbl_name

    [, tbl_name2 TO new_tbl_name2] ...

 

十、ALTER DATABASE语法

常用语法：

Syntax:

ALTER {DATABASE | SCHEMA} [db_name]

    alter_specification ...

ALTER {DATABASE | SCHEMA} db_name

    UPGRADE DATA DIRECTORY NAME