问题
The image below is an example of the icon I am referring to. It is only present on 4 out of 50 databases.
回答1:
That indicates that two or more databases are being grouped together based on a common prefix.
By default, databases with a prefix and underscore are grouped together; so test_keys, test_tables, and test_unicode would all be grouped together under test, to get to each database you'd click the plus sign to expand them.
The separator can be configured with $cfg['NavigationTreeDbSeparator']. There's similar grouping behavior available at the table level with the configuration directive $cfg['NavigationTreeTableSeparator'], and the whole thing can be disabled by setting $cfg['NavigationTreeEnableGrouping'] = 'false';
来源：https://stackoverflow.com/questions/27956560/what-does-the-phpmyadmin-icon-box-of-books-beside-certain-databases-mean