MySQL 5.0 Features - Mastering phpMyAdmin 2.11 for Effective MySQL Management - page 271

Afterwards, the Structure page for our book table reveals a new Triggers section,
which can be used the same way as for routines to edit or delete a trigger:
Testing the Trigger
Contrary to testing stored procedures or functions, there is neither a CALL sequence
nor a function inside a SELECT statement to execute the trigger. Any time the defined
operation (a book INSERT ) happens, the code will execute (in our case, after the
insertion). Therefore, we just have to insert a new book to see the author.total_
page_count column be updated.
Of course, a completely automatic management of this column would involve
creating AFTER UPDATE and AFTER DELETE triggers on the book table.
Information_schema
In the SQL:2003 standard, access to the data dictionary (or database metadata) is
provided by a structure called information_schema . Beacause this is part of the
standard and already exists in other database systems, the decision to implement this
feature into MySQL was a very good one.
MySQL has added some information that is not part of the standard, for
example INFORMATION_SCHEMA.COLUMNS.COLUMN_TYPE . Beware of
that fact if you plan to use this information in a software project that has
to remain portable to other SQL implementations.