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+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
用于存储MySQL服务器、数据库和系统性能等信息。
mysql数据库是MySQL的核心数据库,存储MySQL服务器运行时所需信息,包括数据库的用户、权限设置等控制管理信息。
类似于sql server中的master表。
information_schema数据库存储MySQL服务器中所有数据库的元数据(元数据是关于数据的数据,如数据库名称、表名称、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”)。
information_schema数据库中的表均为视图。
performance_schema数据库在较低级别的运行过程中检查MySQL服务器内部运行状态,监视并收集MySQL服务器时间,用于收集MySQL服务器的性能参数。
sys数据库中的数据用于调优和诊断MySQL实例,是对performance_schema数据库收集的数据的优化处理结果。sys数据库中的对象包括重新组织过的performance_schema数据库数据的视图,用于执行performance_schema数据库配置和生成诊断报告等操作的存储过程,查询performance_schema数据库配置并提供格式化服务和存储函数。
若删除以上系统数据库,则系统无法正常运行。
USE mysql;
SHOW TABLES;
【运行结果】
+---------------------------+ | Tables_in_mysql | +---------------------------+ | columns_priv |- | db | | engine_cost | | event | | func | | general_log | | gtid_executed | | help_category | | help_keyword | | help_relation | | help_topic | | innodb_index_stats | | innodb_table_stats | | ndb_binlog_index | | plugin | | proc | | procs_priv | | proxies_priv | | server_cost | | servers | | slave_master_info | | slave_relay_log_info | | slave_worker_info | | slow_log | | tables_priv | | time_zone | | time_zone_leap_second | | time_zone_name | | time_zone_transition | | time_zone_transition_type | | user | +---------------------------+
查看mysql中的columns_priv表
USE mysql;
SHOW COLUMNS FROM columns_priv FROM mysql;
columns_priv表的内容如下:
+-------------+----------------------------------------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+----------------------------------------------+------+-----+-------------------+-----------------------------+
| Host | char(60) | NO | PRI | | |
| Db | char(64) | NO | PRI | | |
| User | char(32) | NO | PRI | | |
| Table_name | char(64) | NO | PRI | | |
| Column_name | char(64) | NO | PRI | | |
| Timestamp | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
| Column_priv | set('Select','Insert','Update','References') | NO | | | |
+-------------+----------------------------------------------+------+-----+-------------------+-----------------------------+
USE performance_schema;
SHOW TABLES;
运行结果:
+------------------------------------------------------+ | Tables_in_performance_schema | +------------------------------------------------------+ | accounts | | cond_instances | | events_stages_current | | events_stages_history | | events_stages_history_long | | events_stages_summary_by_account_by_event_name | | events_stages_summary_by_host_by_event_name | | events_stages_summary_by_thread_by_event_name | | events_stages_summary_by_user_by_event_name | | events_stages_summary_global_by_event_name | | events_statements_current | | events_statements_history | | events_statements_history_long | | events_statements_summary_by_account_by_event_name | | events_statements_summary_by_digest | | events_statements_summary_by_host_by_event_name | | events_statements_summary_by_program | | events_statements_summary_by_thread_by_event_name | | events_statements_summary_by_user_by_event_name | | events_statements_summary_global_by_event_name | | events_transactions_current | | events_transactions_history | | events_transactions_history_long | | events_transactions_summary_by_account_by_event_name | | events_transactions_summary_by_host_by_event_name | | events_transactions_summary_by_thread_by_event_name | | events_transactions_summary_by_user_by_event_name | | events_transactions_summary_global_by_event_name | | events_waits_current | | events_waits_history | | events_waits_history_long | | events_waits_summary_by_account_by_event_name | | events_waits_summary_by_host_by_event_name | | events_waits_summary_by_instance | | events_waits_summary_by_thread_by_event_name | | events_waits_summary_by_user_by_event_name | | events_waits_summary_global_by_event_name | | file_instances | | file_summary_by_event_name | | file_summary_by_instance | | global_status | | global_variables | | host_cache | | hosts | | memory_summary_by_account_by_event_name | | memory_summary_by_host_by_event_name | | memory_summary_by_thread_by_event_name | | memory_summary_by_user_by_event_name | | memory_summary_global_by_event_name | | metadata_locks | | mutex_instances | | objects_summary_global_by_type | | performance_timers | | prepared_statements_instances | | replication_applier_configuration | | replication_applier_status | | replication_applier_status_by_coordinator | | replication_applier_status_by_worker | | replication_connection_configuration | | replication_connection_status | | replication_group_member_stats | | replication_group_members | | rwlock_instances | | session_account_connect_attrs | | session_connect_attrs | | session_status | | session_variables | | setup_actors | | setup_consumers | | setup_instruments | | setup_objects | | setup_timers | | socket_instances | | socket_summary_by_event_name | | socket_summary_by_instance | | status_by_account | | status_by_host | | status_by_thread | | status_by_user | | table_handles | | table_io_waits_summary_by_index_usage | | table_io_waits_summary_by_table | | table_lock_waits_summary_by_table | | threads | | user_variables_by_thread | | users | | variables_by_thread | +------------------------------------------------------+
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