-- 根据id(有唯一约束的字段)将table2的字段更新到table1
update (select a.f1 a1, a.f2 a2, b.f1 b1, b.f2 b2 
  from table1 a, table2 b where a.id = b.id) 
    set a1 = b1, a2 = b2;