如何在sqlite数据库中检查用户名？ Python

Question

I am trying to check for a username in a data base, when i do it works for the 1st username but after it doesnt work, i think i understand why but i cant work out an alternative. Here is my code:

import sqlite3
conn = sqlite3.connect('tutorial.db')
c = conn.cursor()
def username():
    global limit
    global usernameinput
    usernameinput = input("What would you like your username to be?")
    limit = 0
    select_all_tasks(conn)
def create_table():
    c.execute('CREATE TABLE IF NOT EXISTS stuffToPlot(username TEXT, 
    password TEXT)')
    conn.close
def select_all_tasks(conn):
    global limit
    global passwordinput
    global rows
    c.execute("SELECT * FROM stuffToPlot")
    rows = c.fetchall()
    for row in rows:
        print(row)
    if usernameinput in row:
        print("Username Taken")
        username()
    else:
        if limit < 1:
            passwordinput = input("What would you like your password to 
            be?")
            limit = limit + 1
def data_entry():
    global passwordinput
    global row
    c.execute("INSERT INTO stuffToPlot VALUES(?, ?);",(usernameinput, 
    passwordinput))
    conn.commit()
    c.close()
    conn.close()


create_table()
username()
select_all_tasks(conn)
data_entry()

There is no error, it just doesn't register that the username is already in the database.

Answer 1

You need to indent the if statement and all the following lines to make it work, otherwise only the last row is tested.

for row in rows:
    print(row)
    if usernameinput in row:
        print("Username Taken")

---

Also you could make it simpler :

# select only the field "username" from the table
c.execute("SELECT username FROM stuffToPlot") 
# build a set with all names, from the results given as [('name1',), ('name2',), ('name3',)]
names = {name[0] for name in c.fetchall()} 
if usernameinput in names:  
    print("Username Taken")
    username()
else:
    if limit < 1: