Query Help

I have a ton of records in my xindice database that look like:
<MyRootElement myId="...">.....</MyRootElement>

I need the most efficient way to get a list of all values for myId. How 
can I best do this?

Basically if this was a relational database and I had a table called 
MyRootElement, I'd do "select myId from MyRootElement". I need a xindice 
equivalent.

Thanks in advance,

Liz Glasser