why my else cannoot execute while the statement is else?-CodePudding

my else didn't execute while username and password is wrong. any somebody help me please

def logindb():
print ("=="*15 "\nPlease insert your username and password.")
username = input ("Username : ")
password = input ("Password : ")
cursor.execute(f"SELECT * FROM data WHERE username='{username}' and password='{password}'")
result = cursor.fetchall()
for i in result:
    if (i[0]) == username and (i[1]) == password:
        print ("=="*15 "\n\tLogin Success.\n" "=="*15)
    else:
        print ("=="*15 "\nUsername or password is wrong.\n" "=="*15)

CodePudding user response：

Try changing:

cursor.execute(f"SELECT * FROM data WHERE username='{username}' and password='{password}'")

To:

cursor.execute(f"SELECT username, password FROM data WHERE username='{username}' and password='{password}'")

You're selecting ALL* columns, and if your 0 index column is not username, and your 1 index column is not password, your query result will not match up your submitted username and password.

if (i[0]) == username and (i[1]) == password:

It's also not a good idea to run your SELECT statements wide open if you don't need to. Retrieve only the columns explicitly that you need to retrieve.

CodePudding user response：

You should really use a parameterized query.

But if you are going to use this method of data retrieval then I would go one step further then Griv's answer

cursor.execute(f"SELECT userid FROM data WHERE username='{username}' and password='{password}'")

I would never fetch the username or password. Instead, check for its existence by fetching the primary key of the table.

Then check if that value is null or not.

I am not familiar with python, I assume the f"SELECT is not a typo