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MySQLStudy之--MySQLschema_information数据库_MySQL

时间:2021-07-01 10:21:17 帮助过:6人阅读

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   |     |         |       |
| 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> select table_schema,table_name,table_type,engine,table_rows from tables where table_schema='prod';

+--------------+------------+------------+--------+------------+
| table_schema | table_name | table_type | engine | table_rows |
+--------------+------------+------------+--------+------------+
| prod         | t1         | BASE TABLE | InnoDB |          2 |
| prod         | t2         | BASE TABLE | InnoDB |          2 |
+--------------+------------+------------+--------+------------+
2 rows in set (0.00 sec)
mysql> select * from prod.t1;
+------+-------+
| id   | name  |
+------+-------+
|   10 | tom   |
|   20 | jerry |
|   30 | rose  |
|   40 | ellen |
+------+-------+
4 rows in set (0.00 sec)
mysql> explain select * from prod.t1;
+----+-------------+-------+------+---------------+------+---------+------+------+-------+
| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+------+------+-------+
|  1 | SIMPLE      | t1    | ALL  | NULL          | NULL | NULL    | NULL |    2 | NULL  |
+----+-------------+-------+------+---------------+------+---------+------+------+-------+
1 row in set (0.00 sec)

其中重要的表有:

SCHEMATA表:

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:

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,等等信息。是show tables from schemaname的结果取之此表。

COLUMNS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:

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:

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;

COLLATIONS表提供了关于各字符集的对照信息。

COLLATION_CHARACTER_SET_APPLICABILITY表:

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;

TABLE_CONSTRAINTS表描述了存在约束的表。以及表的约束类型。

KEY_COLUMN_USAGE表:

KEY_COLUMN_USAGE表描述了具有约束的键列。

ROUTINES表:

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:

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;

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。

另外,在未来的版本中会有新的表添加。

【注】information_schema是一个由数据库的元数据组成的数据库。里面存储的是mysql的数据库基本信息。并随时改变。用于查看信息以及系统决策时作为重要的信息提供者。

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