drop table if exists testPrimary;
create table testPrimary
(
 id int,
 stu_name varchar(10),
 remark varchar(50)
);
alter table testPrimary add primary key(id);
show index from testPrimary;
select * from testPrimary ;

执行如下4条insert语句：
insert ignore into testPrimary values (1,'dean','good');
insert ignore into testPrimary values (1,'dean1','good');
insert ignore into testPrimary values (2,'jim','good');
insert ignore into testPrimary values (3,'david','good');
结果：
1    dean    good
2    jim    good
3    david    good
第二条语句执行，但不会报错，也不会insert值