There are three ways to access the DB:

1. $tikilib->query($sql, $attributes); - This method allows you to utilize any functionality your MySQL username is allowed to use. it returns an AdoDB object.
2. PluginSQL
3. PluginDBReport

JQuery gets included at the bottom of the page, so it isn't accessible in your plugins' template. To access JQuery:

1. Make sure you have the global variable $headerlib defined.
2. Add your JS with $headerlib->add_js( your js code );