[Python] How to generate a random number but it should NOT exist in table? [closed]

I need help in creating a code for my own project. It is like a registration site replica but in Python and MySQL.

I need to generate a random number and check if it already exist in table and if it exist generate another number that should also not exist in table.

I have made a code which I think is pretty basic and wrong but a little helpful and I need a code like this only.

import random
import mysql.connector

db = mysql.connector.connect(host="", user="", password="")
cur = db.cursor()

cur.execute("USE iscr")
r = random.randint(1,20)
print(r)
i = str(r)
cur.execute("SELECT sno FROM schedule")
x = str(cur.fetchall())
while i in x:
if i in x:
r = random.randint(1,20)
print(r)
else:
print(r)
break

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