I am starting to write wordpress plug ins, and I have found a scenario where I have to create tables to carry on. Can someone indicate a good tutorial on modifying Wordpress's database?

Their usually excellent documentation appears missing about this subject.

The WordPress Codex includes a good article on creating database tables with Plug ins.

Like Benoit stated, the majority of the occasions wordpress_options is enough, but it is a great help guide to getting began having a custom table if you want it. First though, I'd counsel you to appear and find out whether it can realistically be achieved without developing a new table. Custom Publish Types are designed for the majority of the heavy-lifting for many content-related functions. The foot of the Custom Publish Types Codex entry has several good lessons to get began.

In Wordpress, most plug ins don't create new tables, but make use of the "wordpress_options" table, even if a brand new table could be "natural".

For instance, the "Wordpress acronyms" wordpress plugin. A table with 2 posts (acronym and definition) could be natural. But this wordpress plugin stores the acronyms in one row from the "wordpress_options" table. When information is necessary, this content of the row is parsed and also the fields are removed (utilizing a delimiter). You could look at utilizing the same method.