oracle 代替 update from

钮6070

　　可以用子查询代替
　　update tablea set  a=(select b.a from tableb b,tablea a where a.c=b.c and 限定范围的条件如 b.d in (....))
　　where exists (select 1 from tableb b,tablea a where a.c=b.c and 限定范围的条件如 b.d in (....))
　　例如 这里把表 student_history 的操作时间更新成student_graduate 里的bydate一致 (只是其中2个班级的)
　　update student_history a set operate_date=(select bydate from student_graduate b
where a.class_id=b.class_id
and a.student_id=b.stuid and b.class_id in('ff8080812f52ff02012f8ba5ca053aff','ff8080812f52ff02012f8ba5c9fd3afd'))
where exists (select 1 from student_graduate sg where a.class_id=sg.class_id
and a.student_id=sg.stuid and sg.class_id in('ff8080812f52ff02012f8ba5ca053aff','ff8080812f52ff02012f8ba5c9fd3afd'));