Pre-General Availability Draft: 2017-05-26
Data dictionary tables are invisible and cannot be accessed
directly. However, MySQL supports access to data stored in data
dictionary tables through
INFORMATION_SCHEMA tables and
SHOW statements. For an overview of
the tables that comprise the data dictionary, see
Data Dictionary Tables.
MySQL system tables still exist in MySQL 8.0 and can
be viewed by issuing a
statement on the
mysql system database.
Generally, the difference between MySQL system tables and data
dictionary tables is that system tables contain auxiliary data
such as time zone and help information, whereas data dictionary
tables contain data required to execute SQL queries. MySQL system
tables and data dictionary tables also differ in how they are
upgraded. Upgrading MySQL system tables requires running
mysql_upgrade. Data dictionary upgrades are
managed by MySQL Server.