MySQL Study之--MySQL schema_information数据库
information_schema数据库是在mysql的版本5.0之后产生的，一个虚拟数据库，物理上并不存在。
information_schema数据库类似与“数据字典”，提供了访问数据库元数据的方式，即数据的数据。比如数据库名或表名，列类型，访问权限（更加细化的访问方式）。
案例：
mysql> show databases;
+--------------------+ | Database | +--------------------+ | information_schema | | mysql | | performance_schema | | prod | | test | +--------------------+ 5 rows in set (0.00 sec)访问information_schema：
mysql> use information_schema;
Database changed
mysql> show tables;
+---------------------------------------+ | Tables_in_information_schema | +---------------------------------------+ | CHARACTER_SETS | | COLLATIONS | | COLLATION_CHARACTER_SET_APPLICABILITY | | COLUMNS | | COLUMN_PRIVILEGES | | ENGINES | | EVENTS | | FILES | | GLOBAL_STATUS | | GLOBAL_VARIABLES | | KEY_COLUMN_USAGE | | OPTIMIZER_TRACE | | PARAMETERS | | PARTITIONS | | PLUGINS | | PROCESSLIST | | PROFILING | | REFERENTIAL_CONSTRAINTS | | ROUTINES | | SCHEMATA | | SCHEMA_PRIVILEGES | | SESSION_STATUS | | SESSION_VARIABLES | | STATISTICS | | TABLES | | TABLESPACES | | TABLE_CONSTRAINTS | | TABLE_PRIVILEGES | | TRIGGERS | | USER_PRIVILEGES | | VIEWS | | INNODB_LOCKS | | INNODB_TRX | | INNODB_SYS_DATAFILES | | INNODB_LOCK_WAITS | | INNODB_SYS_TABLESTATS | | INNODB_CMP | | INNODB_METRICS | | INNODB_CMP_RESET | | INNODB_CMP_PER_INDEX | | INNODB_CMPMEM_RESET | | INNODB_FT_DELETED | | INNODB_BUFFER_PAGE_LRU | | INNODB_SYS_FOREIGN | | INNODB_SYS_COLUMNS | | INNODB_SYS_INDEXES | | INNODB_FT_DEFAULT_STOPWORD | | INNODB_SYS_FIELDS | | INNODB_CMP_PER_INDEX_RESET | | INNODB_BUFFER_PAGE | | INNODB_CMPMEM | | INNODB_FT_INDEX_TABLE | | INNODB_FT_BEING_DELETED | | INNODB_SYS_TABLESPACES | | INNODB_FT_INDEX_CACHE | | INNODB_SYS_FOREIGN_COLS | | INNODB_SYS_TABLES | | INNODB_BUFFER_POOL_STATS | | INNODB_FT_CONFIG | +---------------------------------------+ 59 rows in set (0.00 sec)mysql> desc SCHEMATA;
+----------------------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +----------------------------+--------------+------+-----+---------+-------+ | CATALOG_NAME | varchar(512) | NO | | | | | SCHEMA_NAME | varchar(64) | NO | | | | | DEFAULT_CHARACTER_SET_NAME | varchar(32) | NO | | | | | DEFAULT_COLLATION_NAME | varchar(32) | NO | | | | | SQL_PATH | varchar(512) | YES | | NULL | | +----------------------------+--------------+------+-----+---------+-------+ 5 rows in set (0.00 sec)mysql> select SCHEMA_NAME,DEFAULT_CHARACTER_SET_NAME from SCHEMATA;
+--------------------+----------------------------+ | SCHEMA_NAME | DEFAULT_CHARACTER_SET_NAME | +--------------------+----------------------------+ | information_schema | utf8 | | mysql | latin1 | | performance_schema | utf8 | | prod | latin1 | | test | latin1 | +--------------------+----------------------------+ 5 rows in set (0.00 sec)mysql> desc tables;
+-----------------+---------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------------+---------------------+------+-----+---------+-------+ | TABLE_CATALOG | varchar(512) | NO | | | | | TABLE_SCHEMA | varchar(64) | NO | | | | | TABLE_NAME | varchar(64) | NO | | | | | T