yes, I tried it, but the query doesn't return any result. this is my query :
|dbquery "db_sales" "SELECT model, year, product, FROM cars c , product p where v.product=p.idproduct"
| fields model, year, pays, product| where product="$product$"
You are using it right but you can take a look at this http://docs.splunk.com/Documentation/Splunk/6.2.3/Viz/tokens
You probably need to change | where product =$product$ -> | where product ="$product$"
And the token field in input should not contain the space after product, token="product " -> token="product"
Try that and report, glad i could help