For the last few months I've been working on a project that is part website and part data processing.

In theory the website is the bulk of the project, but in practice processing the data has taken a disproportionate amount of resources.

Data exchange with another organisation is always tricky - and in this case we have incoming data that doesn't conform to specification, business rules that change, and a daily data import to run.

The code I've been working on has been through a couple of versions, and now I have in mind a third

Drupal allows you to create multiple sites sharing some or all of the same code and optionally sharing some database tables.

The documentation for the Drupal settings file
http://api.drupal.org/api/file/sites/default/settings.php/5/source

includes the following

<?php
/*
* To have all database names prefixed, set $db_prefix as a string:
*
* $db_prefix = 'main_';
*
* To provide prefixes for specific tables, set $db_prefix as an array.
* The array's keys are the table names and the values are the prefixes.

Comments in code are widely used and generally (but not universally) accepted as a good thing.

Databases can also accommodate comments - but these seem to be very rarely used.

I'm of the opinion that database comments are very useful.

It's often hard to determine the exact meaning of a column - maybe it would be ideal to rename the column but you don't want to risk breaking code.