Hello,

I have a component, let's call it version 1.0. I have that version installed. Later I go back and add some functionality, which includes altering the database tables and adding some columns. Let's call this version 1.1.

So, typically with Joomla you can just upload the new component and it will upgrade the old one. At least, I know it does for the PHP files. What about the database structure? Will Joomla check the tables to see if they match the old tables and alter them if required? This would include adding extra columns and altering a column's properties.

Anyone know? Or am I going to have to go and write an upgrade SQL script? (yuck)

you have to modify few things by hands, jcook is not yet able to manage the component updates, this would surely be a great new funtionality, but for now I suggest you to take a look on this:

J2.5:Managing Component Updates (Update SQL files)