This seems really messy and even wrong but I'm not sure how to optimize it and use best practices

Also, I'm trying to better understand promises and am not sure where and how it is applicable here

const sql = require('mssql');

exports.mssql = (event, context, callback) => {

    sql.connect({
        user: 'user',
        password: 'pass',
        server: 'host',
        database: 'testdb',
        port: 1433,
    },
    err => {
        if (err) {
            console.log("Fail")
            callback('connect failed', err);
        } else {
            let sqlRequest = new sql.Request();
            let sqlQuery = "SELECT * from TestTable;"

            sqlRequest.query(sqlQuery, function(err, data) {
                if (err) {
                    console.log(err)
                }
                console.table(data.recordset);
                console.log(sqlRequest.rowCount);
                sql.close();
            });
            
            callback(null, sqlRequest);

            response = {
                statusCode: 200,
                body: JSON.stringify({
                    message: "Query returned",
                })
            }
            return response;
        }
    })
}