SQL result lengths and showing nothing when searched - mysql

Question

I want my Discord bot to check if a user that joined exists in a MySQL table. However, when it sends the query, it's basically telling me that it doesn't exist even though it should.
This is my current code:
bot.on('guildMemberAdd', async (member) => {
console.log(member.id)
let query = `SELECT userId FROM QR5PVGPh1D.users WHERE userId = '${member.id}'`
let result = connection.query(query)
if(result.length > 0){
console.log("It works!")
}
})

Answer 1

Node is asynchronous, so here you try to console.log result before it has been populated...
You'll find more info in this here :
Node JS MySQL query function not returning result
How do I return callback of MySQL query and push to an array in Node.js?
Here is the code with a callback function. Try it, it should work:
let query = `SELECT userId FROM QR5PVGPh1D.users WHERE userId = '${member.id}'`
connection.query(query, function (err, result) {
if (!err) {
if (result.length > 0) {
console.log("It works!")
}
}
});

Answer 2

Explanation:
As BadSpencer has stated, the mysql driver is asynchronous, and based around callbacks.
Say you're planning on picking your friend up to go to a sporting event. You're not sure when they want you to come, so you call them on the phone and ask them. They think about it for a while, and then tell you a time. You got the information you requested, so you hang up. In programming terms, this would be an example of synchronous code (sometimes thought of as "normal" code in Node.js).
Put yourself back in the same situation. However, when you call your friend this time, they're very busy. You don't want to bother them so you ask them to call you later. You hang up, but now you wait. An hour later, they call you back and tell you the time. This is the thought process of asynchronous code.
There's a lot more that goes on behind the screen, but for simplicity's sake, I'm not going to bombard you with all that information in this answer.
Solutions:
You should pass a function to act as a callback which will use the returned data. Consider this example:
let query = `SELECT userId FROM QR5PVGPh1D.users WHERE userId = '${member.id}'`;
// Passing the callback function as the second parameter.
connection.query(query, (err, result) => {
if (err) return console.error(err);
if (result.length > 0) console.log('It works (it actually does).');
});
However, this callback-based nature can become a nightmare due to the scope of the result and subsequent flow of the code. After a few queries, your code can become messy. To prevent this, you can wrap the query in your own Promise (or use a Promise-based version of the mysql package, like promise-mysql) and await the calls.
Here's an example setup:
// Defining 'connection' as a parameter so
// you can export this function and use it
// anywhere.
function query(connection, sql) {
return new Promise((resolve, reject) => {
connection.query(sql, (err, result) => {
if (err) reject(err);
else resolve(result);
});
});
}
// Asynchronous context needed for 'await' (this needs to be within an async function).
let query = `SELECT userId FROM QR5PVGPh1D.users WHERE userId = '${member.id}'`;
let result = await query(connection, query)
.catch(console.error);