change Shopper Group from default to -Use Default-

[webiedesign]

I have 1700 products where the pricing is all set to the shopper group "Default Shopper Group" and I would like to run a query to change them all to -Use Default-
I *think* this is part of the same issue discussed many time sin this forum where
UPDATE `[prefix]_virtuemart_product_prices` SET `virtuemart_shoppergroup_id`=NULL WHERE 1
is the fix, however, I have tried multiple variations of the query with no success

Joomla! 2.5.22
VirtueMart 2.6.6
no overrides