USE SQL query to count number of categories in a group

So I can figure out how to count the categories that are applied to a specific entry <pre><code>{exp:query sql="SELECT COUNT(*) AS my_count FROM exp_category_posts WHERE entry_id = '{entry_id}’</code></pre>

But I want to extend this so I can count the number of categories in a specific entry that are from a particular category group so for example group_id = “6”

This should be a really simple query, but given I am SQL impaired…. help appreciated.