Benefiting from the Relational System - Mastering phpMyAdmin 3.4 for Effective MySQL Management - page 195

A link ( author_id -> author.id ) appears for each defined relation, and clicking on it
starts verification. For each row, the presence of the corresponding key in the foreign
table is verified and errors, if any, are reported. If the resulting page reports zero
rows, it is good news!
This operation exists because for tables under the storage engines that do not support
foreign key natively, neither MySQL nor phpMyAdmin enforces referential integrity.
It is perfectly possible, for example, to insert data in the book table with invalid
values for author_id column.
Automatic updates of metadata
phpMyAdmin keeps the metadata for internal relations synchronized with every
change that is made to the tables via phpMyAdmin. For example, renaming a
column that is part of a relation would make phpMyAdmin rename this column in
the metadata for the relation. This guarantees that an internal relation continues to
function, even after a column's name is changed. The same thing happens when a
column or table is dropped.
Metadata should be maintained manually in case a change
in the structure is done from outside phpMyAdmin.
Column commenting
Prior to MySQL 4.1, the MySQL structure itself did not support the addition of
comments to a column. Nevertheless, thanks to phpMyAdmin's metadata, we could
comment on columns. However, since MySQL 4.1, native column commenting has
been supported. The good news is that for any MySQL version, column commenting
in phpMyAdmin is always accessed via the Structure page by editing the structure
of each column. In the following example, we need to comment on three columns
of the book table. Hence, we choose them and click on the pencil icon near the With
selected choice.