NodeJS MySQL和Promises无法读取未定义的属性'query‘？

const mysql = require('mysql');

let connection;

function connectToDatabase() {
    return new Promise((resolve, reject) => {
        connection = mysql.createConnection({
            host: 'localhost',
            user: 'your_username',
            password: 'your_password',
            database: 'your_database'
        });

        connection.connect(err => {
            if (err) {
                reject(err);
            } else {
                resolve(connection);
            }
        });
    });
}

connectToDatabase()
    .then(conn => {
        return new Promise((resolve, reject) => {
            conn.query('SELECT * FROM your_table', (error, results) => {
                if (error) {
                    reject(error);
                } else {
                    resolve(results);
                }
            });
        });
    })
    .then(results => {
        console.log(results);
    })
    .catch(err => {
        console.error('Database error:', err);
    });

function executeQuery(queryString) {
    return new Promise((resolve, reject) => {
        if (!connection) {
            reject(new Error('No database connection available.'));
            return;
        }
        connection.query(queryString, (error, results) => {
            if (error) {
                reject(error);
            } else {
                resolve(results);
            }
        });
    });
}

executeQuery('SELECT * FROM your_table')
    .then(results => {
        console.log(results);
    })
    .catch(err => {
        console.error('Query execution failed:', err);
    });