select T.C.value('xm[1]','varchar(20)') as xm,
CAST (case when T.C.value('xb[1]','varchar(20)')='' then 0
else T.C.value('xb[1]','varchar(20)') end as numeric(8,0))as xb
from @lxml_str.nodes('//rtcffx') as T(C)
SELECT T.C.value('xm[1]', 'varchar(20)') AS xm,
CAST((T.C.value('(xb/text())[1]', 'NUMERIC(8, 0)')) AS numeric(8,2)) AS xb
FROM @lxml_str.nodes('//rtcffx') AS T (C)