Subject:Evaluating parameter value Author:Elias Huter Date:30 May 2007 04:36 AM
The * is not interpreted as syntax sign but as the literal '*'. So if a vat_code would be '*' it would be selected. That's why it doesn't work.
One solution would be using xsl:when, like you stated. Other than that you could try to hand over the node itself instead of the "where clause" (not sure if this works, but you can try it):