lubava1991,

GROUP BY T1.ID ? может COUNT должен быть в селекте:

SELECT ID, COUNT(ID) FROM ..... GROUP BY ID

и как и зачем в table () - count(id) - я не очень понимаю, но может быть так:

select t1.id, g1.cnt from LETD.doctype t1, (

select t1.id ID, count(letd.docstore.id) cnt from letd.docstore, xmltable
('$c/data' passing docdata AS "c" columns idnar varchar(200)
path 'formname') as g,
LETD.doctype t1
where docstore.typeid =t1.id and
xmlexists('$c/data[formname!= t1.name]' passing docdata as "c") group by t1.id
) AS G1 where g1.id = t1.id