First of all, I think you are very imprecise when you build the table. The reasons are as follows:
1. You use a nullable field as the primary key
2, and the stu_age field is a character type, but the check is indeed compared with
the value 3, check misspelled
4, The between is misspelled.
If there is no problem with building the table, then inserting data will not be a problem. I tried this in the oracle10g environment.
Of course, inserting data is not rigorous. It is better to replace it with
insert into stu (stu_id, stu_name, stu_sex, stu_age) values('1','whb','m','25');
Your stu table is designed with 5 fields, but you did not write the field table when you inserted it, which means that all insertions are performed, but there are only 4 values behind your values. Of course, there are not enough values to
insert into stu (stu_id, stu_name, stu_sex, stu_age) values('1','whb','m','25');
This is correct, but the last field has no inserted value.