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HomeDatabaseMysql Tutorial(转)MySQL中information_schema是什么_MySQL

大家在安装或使用MYSQL时,会发现除了自己安装的数据库以外,还有一个information_schema数据库。 information_schema数据库是做什么用的呢,使用WordPress博客的朋友可能会想,是不是安装模板添加的数据库呀?看完本片文章 后,你就会对information_schema数据库有所了解。

information_schema数据库是MySQL自带的,它提供了访问数据库元数据的方式。什么是元数据呢?元数据是关于数据的数据,如数据库名或表名,列的数据类型,或访问权限等。有些时候用于表述该信息的其他术语包括“数据词典”和“系统目录”。
在MySQL中,把 information_schema   看作是一个数据库,确切说是信息数据库。其中保存着关于MySQL服务器所维护的所有其他数据库的信息。如数据库名,数据库的表,表栏的数据类型与访问权 限等。在INFORMATION_SCHEMA中,有数个只读表。它们实际上是视图,而不是基本表,因此,你将无法看到与之相关的任何文件。

information_schema数据库表说明:

SCHEMATA表:提供了当前mysql实例中所有数据库的信息。是show databases的结果取之此表。

TABLES表:提供了关于数据库中的表的信息(包括视图)。详细表述了某个表属于哪个schema,表类型,表引擎,创建时间等信息。是show tables from schemaname的结果取之此表。

COLUMNS表:提供了表中的列信息。详细表述了某张表的所有列以及每个列的信息。是show columns from schemaname.tablename的结果取之此表。

STATISTICS表:提供了关于表索引的信息。是show index from schemaname.tablename的结果取之此表。

USER_PRIVILEGES(用户权限)表:给出了关于全程权限的信息。该信息源自mysql.user授权表。是非标准表。

SCHEMA_PRIVILEGES(方案权限)表:给出了关于方案(数据库)权限的信息。该信息来自mysql.db授权表。是非标准表。

TABLE_PRIVILEGES(表权限)表:给出了关于表权限的信息。该信息源自mysql.tables_priv授权表。是非标准表。

COLUMN_PRIVILEGES(列权限)表:给出了关于列权限的信息。该信息源自mysql.columns_priv授权表。是非标准表。

CHARACTER_SETS(字符集)表:提供了mysql实例可用字符集的信息。是SHOW CHARACTER SET结果集取之此表。

COLLATIONS表:提供了关于各字符集的对照信息。

COLLATION_CHARACTER_SET_APPLICABILITY表:指明了可用于校对的字符集。这些列等效于SHOW COLLATION的前两个显示字段。

TABLE_CONSTRAINTS表:描述了存在约束的表。以及表的约束类型。

KEY_COLUMN_USAGE表:描述了具有约束的键列。

ROUTINES表:提供了关于存储子程序(存储程序和函数)的信息。此时,ROUTINES表不包含自定义函数(UDF)。名为“mysql.proc name”的列指明了对应于INFORMATION_SCHEMA.ROUTINES表的mysql.proc表列。

VIEWS表:给出了关于数据库中的视图的信息。需要有show views权限,否则无法查看视图信息。

TRIGGERS表:提供了关于触发程序的信息。必须有super权限才能查看该表

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