When I'm trying to increase the number of characters in first name or last name of Receptionist to be more than 20 characters, This exception happens :

My thoughts :

It would be better to add limits or check the validation of the entered input.

UPDATE

The same problem happens when I'm trying to make an appointment. In First Name, Last Name, and Description sections.

When I'm trying to be a doctor and generating a report from the home page, this problem appears :

I don't know if the problem is happening only with me or with all of you.

In ERD, Schema, and Database, Medical_Stuff should be Medical_Staff.

In Oracle, It's not allowed to type :

Drop Table if exists TableName

In Receptionist
When I'm trying to add a Birthdate with the next year like 2049, it works well without showing a message box. Also, when we do this the age becomes negative as the attached image:

My thoughts :

Try to add a validation function to check the birthdate.

When I'm trying to update the phone number of the Receptionist and put letters instead of numbers, it'll pass without showing any Message Box to tell the user that he should add only numbers.