Get all tables from information_schema, MySQL - mysql

Question

I just dont understand one thing. When I type:
SELECT table_name FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE = 'BASE TABLE';
I get:
+----------------------------------------------+
| table_name |
+----------------------------------------------+
| columns_priv |
| db |
| event |
| func |
| general_log |
| help_category |
| help_keyword |
| help_relation |
| help_topic |
| host |
| ndb_binlog_index |
| plugin |
| proc |
| procs_priv |
| proxies_priv |
| servers |
| slow_log |
| tables_priv |
| time_zone |
| time_zone_leap_second |
| time_zone_name |
| time_zone_transition |
| time_zone_transition_type |
| user |
| cond_instances |
| events_waits_current |
| events_waits_history |
| events_waits_history_long |
| events_waits_summary_by_instance |
| events_waits_summary_by_thread_by_event_name |
| events_waits_summary_global_by_event_name |
| file_instances |
| file_summary_by_event_name |
| file_summary_by_instance |
| mutex_instances |
| performance_timers |
| rwlock_instances |
| setup_consumers |
| setup_instruments |
| setup_timers |
| threads |
+----------------------------------------------+
41 rows in set (0.23 sec)
but selecting seems not to work at all:
mysql> select * from db;
ERROR 1109 (42S02): Unknown table 'db' in information_schema
mysql>
How is that possible? I mean, SELECT table_name FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE = 'BASE TABLE'; showed that there IS a table named 'db' ...
Secondly, when I type: SELECT table_name FROM INFORMATION_SCHEMA.TABLES; it gives me :
+----------------------------------------------+
| table_name |
+----------------------------------------------+
| CHARACTER_SETS |
| COLLATIONS |
| COLLATION_CHARACTER_SET_APPLICABILITY |
| COLUMNS |
| COLUMN_PRIVILEGES |
| ENGINES |
| EVENTS |
| FILES |
| GLOBAL_STATUS |
| GLOBAL_VARIABLES |
| KEY_COLUMN_USAGE |
| 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_BUFFER_PAGE |
| INNODB_TRX |
| INNODB_BUFFER_POOL_STATS |
| INNODB_LOCK_WAITS |
| INNODB_CMPMEM |
| INNODB_CMP |
| INNODB_LOCKS |
| INNODB_CMPMEM_RESET |
| INNODB_CMP_RESET |
| INNODB_BUFFER_PAGE_LRU |
| columns_priv |
| db |
| event |
| func |
| general_log |
| help_category |
| help_keyword |
| help_relation |
| help_topic |
| host |
| ndb_binlog_index |
| plugin |
| proc |
| procs_priv |
| proxies_priv |
| servers |
| slow_log |
| tables_priv |
| time_zone |
| time_zone_leap_second |
| time_zone_name |
| time_zone_transition |
| time_zone_transition_type |
| user |
| cond_instances |
| events_waits_current |
| events_waits_history |
| events_waits_history_long |
| events_waits_summary_by_instance |
| events_waits_summary_by_thread_by_event_name |
| events_waits_summary_global_by_event_name |
| file_instances |
| file_summary_by_event_name |
| file_summary_by_instance |
| mutex_instances |
| performance_timers |
| rwlock_instances |
| setup_consumers |
| setup_instruments |
| setup_timers |
| threads |
+----------------------------------------------+
81 rows in set (0.00 sec)
and Im able to do: mysql> select * from events; and Im getting some results. Why is that? Why can I do select only on upper-case-names? And further, how can I select from information_schema tables given only in uppercase? Cheers
If it matters: Im logged as root to my db.

Answer 1

You select only table_name, but what about table_schema:
MariaDB [(none)]> SELECT table_name, table_schema FROM INFORMATION_SCHEMA.TABLES WHERE
TABLE_TYPE = 'BASE TABLE';
+----------------------------------------------+--------------------+
| table_name | table_schema |
+----------------------------------------------+--------------------+
| columns_priv | mysql |
| db | mysql |
| event | mysql |
| func | mysql |
| general_log | mysql |
| help_category | mysql |
| help_keyword | mysql |
| help_relation | mysql |
| help_topic | mysql |
| host | mysql |
| ndb_binlog_index | mysql |
| plugin | mysql |
| proc | mysql |
| procs_priv | mysql |
| proxies_priv | mysql |
| servers | mysql |
| slow_log | mysql |
| tables_priv | mysql |
| time_zone | mysql |
| time_zone_leap_second | mysql |
| time_zone_name | mysql |
| time_zone_transition | mysql |
| time_zone_transition_type | mysql |
| user | mysql |
| cond_instances | performance_schema |
| events_waits_current | performance_schema |
| events_waits_history | performance_schema |
| events_waits_history_long | performance_schema |
| events_waits_summary_by_instance | performance_schema |
| events_waits_summary_by_thread_by_event_name | performance_schema |
| events_waits_summary_global_by_event_name | performance_schema |
| file_instances | performance_schema |
| file_summary_by_event_name | performance_schema |
| file_summary_by_instance | performance_schema |
| mutex_instances | performance_schema |
| performance_timers | performance_schema |
| rwlock_instances | performance_schema |
| setup_consumers | performance_schema |
| setup_instruments | performance_schema |
| setup_timers | performance_schema |
| threads | performance_schema |
+----------------------------------------------+--------------------+
And you get:
MariaDB [(none)]> select * from mysql.db;
Empty set (0.00 sec)

Answer 2

'information_schema' has ONLY SERVICE INFORMATION. It has info about table 'db' is exist, but it table IS NOT IN 'information_schema' DATABASE -- somewhere, but not in 'information_schema'.
Info about database which has needed table saved in TABLE_SCHEMA field