Changing Data and Structure - Mastering phpMyAdmin 3.4 for Effective MySQL Management - page 92

In the following screenshot, we have modified the structure of the phone column in
the author table, to permit a NULL value (refer to the Editing column attribute section
in this chapter). The Null checkbox is not selected here:
The corresponding data is erased after selecting the Null box.
Applying a function to a value
MySQL language offers some functions that we may apply to data before saving.
Some of these functions appear in a drop-down menu beside each column, if
$cfg['ShowFunctionFields'] is set to TRUE .
The function list is defined in the $cfg['Functions'] array. As usual, the default
values for these arrays are located in libraries/config.default.php . We may
change them by copying the needed section into config.inc.php . If we do so, as
these values can change from version to version, we should take care of merging our
changes with the values of the new version. The most commonly used functions for
a certain data type are displayed first in the list. Some restrictions are defined in the
$cfg['RestrictColumnTypes'] and $cfg['RestrictFunctions'] arrays.