UPDATE DEMO_T1 t1
SET (字段一,字段二,...) = (select 字段一,字段二,... from DEMO_T2 T2 where T2.FNAME = T1.FNAME)
WHERE EXISTS(SELECT 1 FROM DEMO_T2 T2 WHERE T2.FNAME = T1.FNAME);
UPDATE DEMO_T1 t1
SET (字段一,字段二,...) = (select 字段一,字段二,... from DEMO_T2 T2 where T2.FNAME = T1.FNAME)
WHERE EXISTS(SELECT 1 FROM DEMO_T2 T2 WHERE T2.FNAME = T1.FNAME);