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