two dynamic variables on same page

i have set up my site so i have a cf tree with artist as the parent and their album names as the children.......the albums are clickable links that display information dynamically on the page. This was done by setting up a query using WHERE albuminfo=#url.id(primary key for the album information)# and setting up a link from the album name node in the cftree to feed the album info primary key into the url... href='index.cfm?id=#URLEncodedFormat(ID)#'>........

so when i click on the album the album info changes on the screen accordingly..this all works beautifully...

However, I now want to add an index to the page...which will perform the same function of filtering....i have a query

SELECT(List of artists)
FROM (my artist table)
WHERE firstletter= "?"

I have a column in the table called first letter...which contains the first letter of every artist....

I now want set up a clickable link that feeds to the url of the page again...so when i click on (a) the url changes to index.cfm?a

I have got it working to the point where the url changes to index.cfm?a as a test inanother page...but when i have the index in the same page as the cftree, when i click on the index the error message id is undefined appears...which is because no URL parameter for the albuminfo exists when the url is determined by the index letter.

I am unsure of how to arrange this so i can use both in the same page

thanks