MySQL的元数据

今天我们来说下MySQL的元数据,先说说定义和作用:

通过元数据查询结果信息: select、update和delete语句影响的记录数 数据库和数据表的信息: 包含了数据库及数据表的结构信息 MySQL服务器信息: 包含了数据库服务器的当前状态,版本号等 在MySQL的命令提示符中,可以很容易的获取以上服务器信息

数据库和数据表列表 使用 show databases; 或 show tables; 来获取数据库和数据表列表

获取服务器元数据: select version() 服务器版本信息 select database() 当前数据库名(或者返回空) select user() 当前用户名 show status 服务器状态 show variables 服务器配置变量

下面让我们来看看实例:

show databases; +--------------------+ | Database | +--------------------+ | information_schema | | Hello | | World | | mysql | | performance_schema | | sys | +--------------------+ 6 rows in set (0.02 sec)

这是我们之前都学过的,显示数据库列表

mysql> show tables; +-----------------+ | Tables_in_hello | +-----------------+ | cool | | cool_2 | | cool_3 | +-----------------+ 3 rows in set (0.00 sec)

这也是我们之前总用的,显示数据库中有的表

mysql> select version(); +-----------+ | version() | +-----------+ | 5.7.23 | +-----------+ 1 row in set (0.01 sec)

可以查看安装的MySQL的版本

mysql> select database(); +------------+ | database() | +------------+ | hello | +------------+ 1 row in set (0.00 sec)

我们当前选择的数据库

mysql> select user(); +----------------+ | user() | +----------------+ | root@localhost | +----------------+ 1 row in set (0.00 sec)

查看现在的使用者,一般就是 localhost

mysql> show status; +-----------------------------------------------+--------------------------------------------------+ | Variable_name | Value | +-----------------------------------------------+--------------------------------------------------+ | Aborted_clients | 2 | | Aborted_connects | 1 | | Binlog_cache_disk_use | 0 | | Binlog_cache_use | 0 | | Binlog_stmt_cache_disk_use | 0 | | Binlog_stmt_cache_use | 0 | | Bytes_received | 455 | | Bytes_sent | 1952 | | Com_admin_commands | 0 | | Com_assign_to_keycache | 0 | | Com_alter_db | 0 | | Com_alter_db_upgrade | 0 | | Com_alter_event | 0 | | Com_alter_function | 0 | | Com_alter_instance | 0 | | Com_alter_procedure | 0 | | Com_alter_server | 0 | | Com_alter_table | 0 | | Com_alter_tablespace | 0 | | Com_alter_user | 0 | | Com_analyze | 0 | | Com_begin | 0 | | Com_binlog | 0 | | Com_call_procedure | 0 | | Com_change_db | 1 | | Com_change_master | 0 | | Com_change_repl_filter | 0 | | Com_check | 0 | | Com_checksum | 0 | | Com_commit | 0 | | Com_create_db | 0 | | Com_create_event | 0 | | Com_create_function | 0 | | Com_create_index | 0 | | Com_create_procedure | 0 | | Com_create_server | 0 | | Com_create_table | 0 | | Com_create_trigger | 0 | | Com_create_udf | 0 | | Com_create_user | 0 | | Com_create_view | 0 | | Com_dealloc_sql | 0 | | Com_delete | 0 | | Com_delete_multi | 0 | | Com_do | 0 | | Com_drop_db | 0 | | Com_drop_event | 0 | | Com_drop_function | 0 | | Com_drop_index | 0 | | Com_drop_procedure | 0 | | Com_drop_server | 0 | | Com_drop_table | 0 | | Com_drop_trigger | 0 | | Com_drop_user | 0 | | Com_drop_view | 0 | | Com_empty_query | 0 | | Com_execute_sql | 0 | | Com_explain_other | 0 | | Com_flush | 0 | | Com_get_diagnostics | 0 | | Com_grant | 0 | | Com_ha_close | 0 | | Com_ha_open | 0 | | Com_ha_read | 0 | | Com_help | 0 | | Com_insert | 0 | | Com_insert_select | 0 | | Com_install_plugin | 0 | | Com_kill | 0 | | Com_load | 0 | | Com_lock_tables | 0 | | Com_optimize | 0 | | Com_preload_keys | 0 | | Com_prepare_sql | 0 | | Com_purge | 0 | | Com_purge_before_date | 0 | | Com_release_savepoint | 0 | | Com_rename_table | 0 | | Com_rename_user | 0 | | Com_repair | 0 | | Com_replace | 0 | | Com_replace_select | 0 | | Com_reset | 0 | | Com_resignal | 0 | | Com_revoke | 0 | | Com_revoke_all | 0 | | Com_rollback | 0 | | Com_rollback_to_savepoint | 0 | | Com_savepoint | 0 | | Com_select | 5 | | Com_set_option | 0 | | Com_signal | 0 | | Com_show_binlog_events | 0 | | Com_show_binlogs | 0 | | Com_show_charsets | 0 | | Com_show_collations | 0 | | Com_show_create_db | 0 | | Com_show_create_event | 0 | | Com_show_create_func | 0 | | Com_show_create_proc | 0 | | Com_show_create_table | 0 | | Com_show_create_trigger | 0 | | Com_show_databases | 2 | | Com_show_engine_logs | 0 | | Com_show_engine_mutex | 0 | | Com_show_engine_status | 0 | | Com_show_events | 0 | | Com_show_errors | 0 | | Com_show_fields | 3 | | Com_show_function_code | 0 | | Com_show_function_status | 0 | | Com_show_grants | 0 | | Com_show_keys | 0 | | Com_show_master_status | 0 | | Com_show_open_tables | 0 | | Com_show_plugins | 0 | | Com_show_privileges | 0 | | Com_show_procedure_code | 0 | | Com_show_procedure_status | 0 | | Com_show_processlist | 0 | | Com_show_profile | 0 | | Com_show_profiles | 0 | | Com_show_relaylog_events | 0 | | Com_show_slave_hosts | 0 | | Com_show_slave_status | 0 | | Com_show_status | 1 | | Com_show_storage_engines | 0 | | Com_show_table_status | 0 | | Com_show_tables | 2 | | Com_show_triggers | 0 | | Com_show_variables | 0 | | Com_show_warnings | 0 | | Com_show_create_user | 0 | | Com_shutdown | 0 | | Com_slave_start | 0 | | Com_slave_stop | 0 | | Com_group_replication_start | 0 | | Com_group_replication_stop | 0 | | Com_stmt_execute | 0 | | Com_stmt_close | 0 | | Com_stmt_fetch | 0 | | Com_stmt_prepare | 0 | | Com_stmt_reset | 0 | | Com_stmt_send_long_data | 0 | | Com_truncate | 0 | | Com_uninstall_plugin | 0 | | Com_unlock_tables | 0 | | Com_update | 0 | | Com_update_multi | 0 | | Com_xa_commit | 0 | | Com_xa_end | 0 | | Com_xa_prepare | 0 | | Com_xa_recover | 0 | | Com_xa_rollback | 0 | | Com_xa_start | 0 | | Com_stmt_reprepare | 0 | | Compression | OFF | | Connection_errors_accept | 0 | | Connection_errors_internal | 0 | | Connection_errors_max_connections | 0 | | Connection_errors_peer_address | 0 | | Connection_errors_select | 0 | | Connection_errors_tcpwrap | 0 | | Connections | 9 | | Created_tmp_disk_tables | 0 | | Created_tmp_files | 5 | | Created_tmp_tables | 4 | | Delayed_errors | 0 | | Delayed_insert_threads | 0 | | Delayed_writes | 0 | | Flush_commands | 1 | | Handler_commit | 0 | | Handler_delete | 0 | | Handler_discover | 0 | | Handler_external_lock | 0 | | Handler_mrr_init | 0 | | Handler_prepare | 0 | | Handler_read_first | 0 | | Handler_read_key | 0 | | Handler_read_last | 0 | | Handler_read_next | 0 | | Handler_read_prev | 0 | | Handler_read_rnd | 0 | | Handler_read_rnd_next | 22 | | Handler_rollback | 0 | | Handler_savepoint | 0 | | Handler_savepoint_rollback | 0 | | Handler_update | 0 | | Handler_write | 18 | | Innodb_buffer_pool_dump_status | Dumping of buffer pool not started | | Innodb_buffer_pool_load_status | Buffer pool(s) load completed at 200719 11:29:09 | | Innodb_buffer_pool_resize_status | | | Innodb_buffer_pool_pages_data | 341 | | Innodb_buffer_pool_bytes_data | 5586944 | | Innodb_buffer_pool_pages_dirty | 0 | | Innodb_buffer_pool_bytes_dirty | 0 | | Innodb_buffer_pool_pages_flushed | 61 | | Innodb_buffer_pool_pages_free | 7851 | | Innodb_buffer_pool_pages_misc | 0 | | Innodb_buffer_pool_pages_total | 8192 | | Innodb_buffer_pool_read_ahead_rnd | 0 | | Innodb_buffer_pool_read_ahead | 0 | | Innodb_buffer_pool_read_ahead_evicted | 0 | | Innodb_buffer_pool_read_requests | 1477 | | Innodb_buffer_pool_reads | 305 | | Innodb_buffer_pool_wait_free | 0 | | Innodb_buffer_pool_write_requests | 388 | | Innodb_data_fsyncs | 16 | | Innodb_data_pending_fsyncs | 0 | | Innodb_data_pending_reads | 0 | | Innodb_data_pending_writes | 0 | | Innodb_data_read | 5067264 | | Innodb_data_reads | 332 | | Innodb_data_writes | 84 | | Innodb_data_written | 1084928 | | Innodb_dblwr_pages_written | 5 | | Innodb_dblwr_writes | 4 | | Innodb_log_waits | 0 | | Innodb_log_write_requests | 0 | | Innodb_log_writes | 4 | | Innodb_os_log_fsyncs | 7 | | Innodb_os_log_pending_fsyncs | 0 | | Innodb_os_log_pending_writes | 0 | | Innodb_os_log_written | 2048 | | Innodb_page_size | 16384 | | Innodb_pages_created | 37 | | Innodb_pages_read | 304 | | Innodb_pages_written | 61 | | Innodb_row_lock_current_waits | 0 | | Innodb_row_lock_time | 0 | | Innodb_row_lock_time_avg | 0 | | Innodb_row_lock_time_max | 0 | | Innodb_row_lock_waits | 0 | | Innodb_rows_deleted | 0 | | Innodb_rows_inserted | 2 | | Innodb_rows_read | 10 | | Innodb_rows_updated | 0 | | Innodb_num_open_files | 19 | | Innodb_truncated_status_writes | 0 | | Innodb_available_undo_logs | 128 | | Key_blocks_not_flushed | 0 | | Key_blocks_unused | 6693 | | Key_blocks_used | 6 | | Key_read_requests | 28 | | Key_reads | 5 | | Key_write_requests | 24 | | Key_writes | 4 | | Last_query_cost | 0.000000 | | Last_query_partial_plans | 0 | | Locked_connects | 0 | | Max_execution_time_exceeded | 0 | | Max_execution_time_set | 0 | | Max_execution_time_set_failed | 0 | | Max_used_connections | 1 | | Max_used_connections_time | 2020-07-20 22:49:33 | | Not_flushed_delayed_rows | 0 | | Ongoing_anonymous_transaction_count | 0 | | Open_files | 29 | | Open_streams | 0 | | Open_table_definitions | 108 | | Open_tables | 111 | | Opened_files | 180 | | Opened_table_definitions | 0 | | Opened_tables | 3 | | Performance_schema_accounts_lost | 0 | | Performance_schema_cond_classes_lost | 0 | | Performance_schema_cond_instances_lost | 0 | | Performance_schema_digest_lost | 0 | | Performance_schema_file_classes_lost | 0 | | Performance_schema_file_handles_lost | 0 | | Performance_schema_file_instances_lost | 0 | | Performance_schema_hosts_lost | 0 | | Performance_schema_index_stat_lost | 0 | | Performance_schema_locker_lost | 0 | | Performance_schema_memory_classes_lost | 0 | | Performance_schema_metadata_lock_lost | 0 | | Performance_schema_mutex_classes_lost | 0 | | Performance_schema_mutex_instances_lost | 0 | | Performance_schema_nested_statement_lost | 0 | | Performance_schema_prepared_statements_lost | 0 | | Performance_schema_program_lost | 0 | | Performance_schema_rwlock_classes_lost | 0 | | Performance_schema_rwlock_instances_lost | 0 | | Performance_schema_session_connect_attrs_lost | 0 | | Performance_schema_socket_classes_lost | 0 | | Performance_schema_socket_instances_lost | 0 | | Performance_schema_stage_classes_lost | 0 | | Performance_schema_statement_classes_lost | 0 | | Performance_schema_table_handles_lost | 0 | | Performance_schema_table_instances_lost | 0 | | Performance_schema_table_lock_stat_lost | 0 | | Performance_schema_thread_classes_lost | 0 | | Performance_schema_thread_instances_lost | 0 | | Performance_schema_users_lost | 0 | | Prepared_stmt_count | 0 | | Qcache_free_blocks | 1 | | Qcache_free_memory | 1031832 | | Qcache_hits | 0 | | Qcache_inserts | 0 | | Qcache_lowmem_prunes | 0 | | Qcache_not_cached | 20 | | Qcache_queries_in_cache | 0 | | Qcache_total_blocks | 1 | | Queries | 86 | | Questions | 14 | | Select_full_join | 0 | | Select_full_range_join | 0 | | Select_range | 0 | | Select_range_check | 0 | | Select_scan | 4 | | Slave_open_temp_tables | 0 | | Slow_launch_threads | 0 | | Slow_queries | 0 | | Sort_merge_passes | 0 | | Sort_range | 0 | | Sort_rows | 0 | | Sort_scan | 0 | | Ssl_accept_renegotiates | 0 | | Ssl_accepts | 0 | | Ssl_callback_cache_hits | 0 | | Ssl_cipher | | | Ssl_cipher_list | | | Ssl_client_connects | 0 | | Ssl_connect_renegotiates | 0 | | Ssl_ctx_verify_depth | 0 | | Ssl_ctx_verify_mode | 0 | | Ssl_default_timeout | 0 | | Ssl_finished_accepts | 0 | | Ssl_finished_connects | 0 | | Ssl_server_not_after | | | Ssl_server_not_before | | | Ssl_session_cache_hits | 0 | | Ssl_session_cache_misses | 0 | | Ssl_session_cache_mode | NONE | | Ssl_session_cache_overflows | 0 | | Ssl_session_cache_size | 0 | | Ssl_session_cache_timeouts | 0 | | Ssl_sessions_reused | 0 | | Ssl_used_session_cache_entries | 0 | | Ssl_verify_depth | 0 | | Ssl_verify_mode | 0 | | Ssl_version | | | Table_locks_immediate | 108 | | Table_locks_waited | 0 | | Table_open_cache_hits | 0 | | Table_open_cache_misses | 3 | | Table_open_cache_overflows | 0 | | Tc_log_max_pages_used | 0 | | Tc_log_page_size | 0 | | Tc_log_page_waits | 0 | | Threads_cached | 0 | | Threads_connected | 1 | | Threads_created | 1 | | Threads_running | 1 | | Uptime | 359714 | | Uptime_since_flush_status | 359714 | +-----------------------------------------------+--------------------------------------------------+ 356 rows in set (0.04 sec)

显示MySQL服务器状态

mysql> show variables;

        |

| version_compile_os | macos10.13 | | wait_timeout | 28800 | | warning_count | 0 |

可以试下,有513项

好的,今天就先到这里吧

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