The following is extremely slow over one network (23 seconds), whereas at other sites takes less than 1 sec.
Patx is a DBF with 28,000 records (indexed on patuid)
TmpSync is a cursor with one record

UPDATE patx ;
FROM tmpSync ;
SET ;
	patx.ins = tmpSync.inscode + tmpSync.feecode, ;
	patx.pgroup = tmpSync.groupid ;
WHERE patx.patuid = tmpSync.patuid

I was under the impression that UPDATE SQL locks records, as needed, but that may not be so. SCAN / REPLACE is much faster in my tests.