检查 MySQL 中是否存在值

Question

I am developing a user authentication system with expressjs. Therefore to store user data i use a mysql database... When I query to my database I do it with this: SELECT password FROM USERS WHERE email=EmailHere
The problem with this is I dont know an elegant solution to returning an error message if the email doesnt exist. Somewhat understandable?

So to conclude : I want to know if that value exists when I query to the db so I dont get an error message.

Edit:

 const query = `SELECT password FROM USERS WHERE email=?;`; let [rows, fields] = await db.promise().query(query, [req.body.email]); const password = rows[0].password; console.log(password);

This gives me the error: Cannot read properties of undefined reading 'password'.

So it is trying to access the.password column. Can I prevent that?

Thanks in advance Have a great day

Answer 1

Ok it turns out:

If I check if the length of the rows Array > 0 it fixes the problem. In the else statement I can just log out an error message to say the user does not exist. This could look something like this:

 if (.rows.length > 0) return res.status(400);send('User doensnt exist.'); const password = rows[0].password // Declaring the variable after I know it exists

Thanks to @danblack for this answer