How can I optimize my Telebot program to handle multiple users with SQLite database?

Question

I made a shop/bot. I use database to filter out data. But when two or more people use my bot - it start to lag and don't send messages. And console send multiple messages of ids.

import telebot
from telebot import types
import sqlite3

db = sqlite3.connect('database.db', check_same_thread = False)
sql = db.cursor()
sql.execute("""CREATE TABLE IF NOT EXISTS users(
    chatid TEXT,
    username TEXT,
    balance INT
    tovary TEXT
)""")
db.commit()

bot = telebot.TeleBot('Token')

mainmenu = types.ReplyKeyboardMarkup(resize_keyboard=True, row_width=2)
rules = types.KeyboardButton('Rules')
shop = types.KeyboardButton('Shop')
reviews = types.KeyboardButton('Reviews')
profile = types.KeyboardButton('Profile')
close = types.KeyboardButton('Close')
mainmenu.add(rules, shop, reviews, profile, close)

@bot.message_handler(commands=['start'])
def start(message):
    def start(message):
        greeting = f'<b>Test greeting</b>'
        bot.send_message(message.chat.id, f'{greeting}', parse_mode='html', reply_markup=mainmenu)
    sql.execute(f"SELECT chatid FROM users WHERE chatid = '{message.chat.id}'")
    if sql.fetchone() is None:
        sql.execute(f"INSERT INTO users VALUES(?,?,?)", (message.chat.id, message.from_user.username, 0))
        db.commit()
    else:
        for value in sql.execute("SELECT * FROM users"):
            print(value)

@bot.message_handler(content_types=['text'])
def handler(message):
    if message.text == "$money.test":
        sql.execute(f"UPDATE users SET balance = balance + 100 WHERE chatid = {message.chat.id}")
        db.commit()
        for value in sql.execute(f"SELECT balance FROM users WHERE chatid = {message.chat.id}"):
            bot.send_message(message.chat.id, f"Хорошо, я выдал тебе 100 гривен на баланс.\n\nТвой баланс: {value[0]}", parse_mode='html')
    elif message.text == "$del.account":
        sql.execute(f"DELETE FROM users WHERE chatid = {message.chat.id}")
        db.commit()
        bot.send_message(message.chat.id, "Аккаунт удалён.")

bot.polling(none_stop=True)

This is photo of console. enter image description here This is photo of telegram. enter image description here

What should I do to work with multiple users?