Python SQLite3删除另一个条目时更新主键

Question

Currently I am using a database for a student music lesson planner.

Whenever I delete a student from the database and then I add a new student why doesn't it add the new student with the ID of 1?

The code for adding data is as follows:

def add():
  add = 'y'
  while add == 'y':
    Name = input("Please enter the name of the student: ")
    Year =  int(input("Please enter the students year: "))
    Student = (Name,Year)       
    insert_data(Student)
    print("New data added")
    print()
    add = input("Do you wish to add another student? (y/n) ")
  display = menu.Menu.DisplayMenu("Student") #Adding student name to menu
  choice = GetMenuChoice() #Getting the user's menu choice
  ValidateMenuChoice(choice) #Validating that user choice
  main(choice) #Passing in choice into the main variable

def insert_data(values):
    with sqlite3.connect("records.db")as db:
        cursor = db.cursor()
        sql = "Insert into Student(Name,Year)values(?,?)"
        cursor.execute(sql,values)
        db.commit()

and the database code is:

def create_student_table():  
    sql = """create table Student
            (StudentID integer,
             Name string,
             Year integer,
             primary key(StudentID))"""
    create_table(db_name,"Student",sql)

Any help would be greatly appreciated!

Answer 1

That's how most databases work; sequences only ever produce new values and not reuse old values.

This is both more efficient (not having to search for free ids) and a good idea. Imagine a system that integrates multiple parts, including your database. Then the User ID you just deleted could still be referenced in other systems as well. If your database would reuse the ID when creating a new user, suddenly those external systems are referring to a new user, leading to hard-to-untangle bugs.

If you must reuse numbers, then you'll have to specify an id to use explicitly instead of having the database pick one for you. You'll have to find your own 'missing' numbers in that case, which will be difficult if you are using the database from more than one thread or process.

Also see the SQLite auto-incrementation documentation for some more detail on how you can influence how new values are picked; you either get monotonically increasing numbers (which can produce gaps) or, if you add the AUTOINCREMENT keyword, a value to be guaranteed to be 'highest value ever used plus 1'.

Note that the default behaviour is to automatically generate a ROWID that is 1 higher than the values currently in use:

If no ROWID is specified on the insert, or if the specified ROWID has a value of NULL , then an appropriate ROWID is created automatically. The usual algorithm is to give the newly created row a ROWID that is one larger than the largest ROWID in the table prior to the insert.

The normal ROWID selection algorithm described above will generate monotonically increasing unique ROWIDs as long as you never use the maximum ROWID value and you never delete the entry in the table with the largest ROWID . If you ever delete rows or if you ever create a row with the maximum possible ROWID , then ROWIDs from previously deleted rows might be reused when creating new rows and newly created ROWID s might not be in strictly ascending order.

Emphasis mine.