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标题：MYSQL小白的FAQ系列—-6—-如何查看mysql中的“元数据”(类似于oracle的数据字典)
作者：Lunar©版权所有[文章允许转载,但必须以链接方式注明源地址,否则追究法律责任.]
mysql中，INFORMATION_SCHEMA提供了访问数据库元数据的方式.
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mysql5.5的官方文档中有以下内容：
第23章：INFORMATION_SCHEMA信息数据库
目录
23.1. INFORMATION_SCHEMA表
23.1.1. INFORMATION_SCHEMA SCHEMATA表
23.1.2. INFORMATION_SCHEMA TABLES表
23.1.3. INFORMATION_SCHEMA COLUMNS表
23.1.4. INFORMATION_SCHEMA STATISTICS表
23.1.5. INFORMATION_SCHEMA USER_PRIVILEGES表
23.1.6. INFORMATION_SCHEMA SCHEMA_PRIVILEGES表
23.1.7. INFORMATION_SCHEMA TABLE_PRIVILEGES表
23.1.8. INFORMATION_SCHEMA COLUMN_PRIVILEGES表
23.1.9. INFORMATION_SCHEMA CHARACTER_SETS表
23.1.10. INFORMATION_SCHEMA COLLATIONS表
23.1.11. INFORMATION_SCHEMA COLLATION_CHARACTER_SET_APPLICABILITY表
23.1.12. INFORMATION_SCHEMA TABLE_CONSTRAINTS表
23.1.13. INFORMATION_SCHEMA KEY_COLUMN_USAGE表
23.1.14. INFORMATION_SCHEMA ROUTINES表
23.1.15. INFORMATION_SCHEMA VIEWS表
23.1.16. INFORMATION_SCHEMA TRIGGERS表
23.1.17. 其他INFORMATION_SCHEMA表
information_schema数据库是MySQL自带的(貌似mysql 5以后才有的)，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。
mysql> use information_schema; Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed mysql> desc information_schema.tables; +-----------------+---------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------------+---------------------+------+-----+---------+-------+ | TABLE_CATALOG | varchar(512) | NO | | | | | TABLE_SCHEMA | varchar(64) | NO | | | | | TABLE_NAME | varchar(64) | NO | | | | | TABLE_TYPE | varchar(64) | NO | | | | | ENGINE | varchar(64) | YES | | NULL | | | VERSION | bigint(21) unsigned | YES | | NULL | | | ROW_FORMAT | varchar(10) | YES | | NULL | | | TABLE_ROWS | bigint(21) unsigned | YES | | NULL | | | AVG_ROW_LENGTH | bigint(21) unsigned | YES | | NULL | | | DATA_LENGTH | bigint(21) unsigned | YES | | NULL | | | MAX_DATA_LENGTH | bigint(21) unsigned | YES | | NULL | | | INDEX_LENGTH | bigint(21) unsigned | YES | | NULL | | | DATA_FREE | bigint(21) unsigned | YES | | NULL | | | AUTO_INCREMENT | bigint(21) unsigned | YES | | NULL | | | CREATE_TIME | datetime | YES | | NULL | | | UPDATE_TIME | datetime | YES | | NULL | | | CHECK_TIME | datetime | YES | | NULL | | | TABLE_COLLATION | varchar(32) | YES | | NULL | | | CHECKSUM | bigint(21) unsigned | YES | | NULL | | | CREATE_OPTIONS | varchar(255) | YES | | NULL | | | TABLE_COMMENT | varchar(2048) | NO | | | | +-----------------+---------------------+------+-----+---------+-------+ 21 rows in set (0.00 sec) mysql>
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
mysql> SELECT table_name, table_schema,table_type, engine
-> FROM information_schema.tables;
+---------------------------------------+--------------------+-------------+--------+
| table_name | table_schema | table_type | engine |
+---------------------------------------+--------------------+-------------+--------+
| CHARACTER_SETS | information_schema | SYSTEM VIEW | MEMORY |
| COLLATIONS | information_schema | SYSTEM VIEW | MEMORY |
| COLLATION_CHARACTER_SET_APPLICABILITY | information_schema | SYSTEM VIEW | MEMORY |
| COLUMNS | information_schema | SYSTEM VIEW | MyISAM |
| COLUMN_PRIVILEGES | information_schema | SYSTEM VIEW | MEMORY |
| ENGINES | information_schema | SYSTEM VIEW | MEMORY |
| EVENTS | information_schema | SYSTEM VIEW | MyISAM |
| FILES | information_schema | SYSTEM VIEW | MEMORY |
| GLOBAL_STATUS | information_schema | SYSTEM VIEW | MEMORY |
| GLOBAL_VARIABLES | information_schema | SYSTEM VIEW | MEMORY |
| KEY_COLUMN_USAGE | information_schema | SYSTEM VIEW | MEMORY |
| OPTIMIZER_TRACE | information_schema | SYSTEM VIEW | MyISAM |
| PARAMETERS | information_schema | SYSTEM VIEW | MyISAM |
| PARTITIONS | information_schema | SYSTEM VIEW | MyISAM |
| PLUGINS | information_schema | SYSTEM VIEW | MyISAM |
| PROCESSLIST | information_schema | SYSTEM VIEW | MyISAM |
| PROFILING | information_schema | SYSTEM VIEW | MEMORY |
| REFERENTIAL_CONSTRAINTS | information_schema | SYSTEM VIEW | MEMORY |
| ROUTINES | information_schema | SYSTEM VIEW | MyISAM |
| SCHEMATA | information_schema | SYSTEM VIEW | MEMORY |
| SCHEMA_PRIVILEGES | information_schema | SYSTEM VIEW | MEMORY |
| SESSION_STATUS | information_schema | SYSTEM VIEW | MEMORY |
| SESSION_VARIABLES | information_schema | SYSTEM VIEW | MEMORY |
| STATISTICS | information_schema | SYSTEM VIEW | MEMORY |
| TABLES | information_schema | SYSTEM VIEW | MEMORY |
| TABLESPACES | information_schema | SYSTEM VIEW | MEMORY |
| TABLE_CONSTRAINTS | information_schema | SYSTEM VIEW | MEMORY |
| TABLE_PRIVILEGES | information_schema | SYSTEM VIEW | MEMORY |
| TRIGGERS | information_schema | SYSTEM VIEW | MyISAM |
| USER_PRIVILEGES | information_schema | SYSTEM VIEW | MEMORY |
| VIEWS | information_schema | SYSTEM VIEW | MyISAM |
| INNODB_LOCKS | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_TRX | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_SYS_DATAFILES | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_LOCK_WAITS | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_SYS_TABLESTATS | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_CMP | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_METRICS | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_CMP_RESET | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_CMP_PER_INDEX | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_CMPMEM_RESET | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_FT_DELETED | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_BUFFER_PAGE_LRU | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_SYS_FOREIGN | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_SYS_COLUMNS | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_SYS_INDEXES | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_FT_DEFAULT_STOPWORD | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_SYS_FIELDS | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_CMP_PER_INDEX_RESET | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_BUFFER_PAGE | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_CMPMEM | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_FT_INDEX_TABLE | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_FT_BEING_DELETED | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_SYS_TABLESPACES | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_FT_INDEX_CACHE | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_SYS_FOREIGN_COLS | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_SYS_TABLES | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_BUFFER_POOL_STATS | information_schema | SYSTEM VIEW | MEMORY |
| INNODB_FT_CONFIG | information_schema | SYSTEM VIEW | MEMORY |
| columns_priv | mysql | BASE TABLE | MyISAM |
| db | mysql | BASE TABLE | MyISAM |
| event | mysql | BASE TABLE | MyISAM |
| func | mysql | BASE TABLE | MyISAM |
| general_log | mysql | BASE TABLE | CSV |
| help_category | mysql | BASE TABLE | MyISAM |
| help_keyword | mysql | BASE TABLE | MyISAM |
| help_relation | mysql | BASE TABLE | MyISAM |
| help_topic | mysql | BASE TABLE | MyISAM |
| innodb_index_stats | mysql | BASE TABLE | InnoDB |
| innodb_table_stats | mysql | BASE TABLE | InnoDB |
| ndb_binlog_index | mysql | BASE TABLE | MyISAM |
| plugin | mysql | BASE TABLE | MyISAM |
| proc | mysql | BASE TABLE | MyISAM |
| procs_priv | mysql | BASE TABLE | MyISAM |
| proxies_priv | mysql | BASE TABLE | MyISAM |
| servers | mysql | BASE TABLE | MyISAM |
| slave_master_info | mysql | BASE TABLE | InnoDB |
| slave_relay_log_info | mysql | BASE TABLE | InnoDB |
| slave_worker_info | mysql | BASE TABLE | InnoDB |
| slow_log | mysql | BASE TABLE | CSV |
| tables_priv | mysql | BASE TABLE | MyISAM |
| time_zone | mysql | BASE TABLE | MyISAM |
| time_zone_leap_second | mysql | BASE TABLE | MyISAM |
| time_zone_name | mysql | BASE TABLE | MyISAM |
| time_zone_transition | mysql | BASE TABLE | MyISAM |
| time_zone_transition_type | mysql | BASE TABLE | MyISAM |
| user | mysql | BASE TABLE | MyISAM |
+---------------------------------------+--------------------+-------------+--------+
87 rows in set (0.01 sec)
mysql>
SELECT table_name, table_schema,table_type, engine
FROM information_schema.tables
WHERE table_schema = 'mysql'
ORDER BY table_name DESC;
INFORMATION_SCHEMA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。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。
每位MySQL用户均有权访问这些表，但仅限于表中的特定行，在这类行中含有用户具有恰当访问权限的对象。
