MySQL 存储过程中执行动态SQL语句的方法

drop PROCEDURE if exists my_procedure; 
create PROCEDURE my_procedure() 
BEGIN 
  declare my_sqll varchar(500); 
  set my_sqll="select * from aa_list"; 
 set @ms=my_sqll; 
 PREPARE s1 from @ms; 
 EXECUTE s1; 
 deallocate prepare s1; 
end;
drop PROCEDURE if exist