SET @xml = 
'
'

DECLARE @xml xml;
DECLARE @expression nvarchar(128);
SET @xml = 
'<books>
<book price=''31'' name=''SQL Server Central'' Author=''Steve Jones''/>
</books>';

--SET @expression = '/books/book/@price[text()=31]';


IF @xml.exist('/books/book/@price[text()=31]') =1
 SELECT 
 T.value('./@price[1]','int'),
 T.value('./@name[1]','nvarchar(32)'),
 T.value('./@Author[1]','nvarchar(32)')
 FROM @xml.nodes('/books/book') AS T(T);

/books/book/@price=31