UPDATE bperadm t1
SET (t1.cdagrupr) = (SELECT lpad(t2.cdprov,6 ,'0')
FROM bpersona t2
WHERE t1.cddni = t2.cddni)
WHERE EXISTS (
SELECT 1
FROM bpersona t2
WHERE t1.cddni = t2.cddni )
AND t1.cdsitnom=0
Aquí lo tienes
UPDATE table1 t1
SET (name, desc) = (SELECT t2.name, t2.desc
FROM table2 t2
WHERE t1.id = t2.id)
WHERE EXISTS (
SELECT 1
FROM table2 t2
WHERE t1.id = t2.id )