Check if user already exist in MySql database in Node.js

Question

I am new to Node.js and SQL programming and I encountered a problem where I don't know how to get, if the user already exists in the database. I tried to check if (selectUsername.length = username) and it didn't work. I also tried with the version from a previous post in stackoverflow

 const selectUsername = conn.query("SELECT username FROM user WHERE username= "+ username, function (err, row){
        if (row && row.length) {
          console.log('Case row was found!');
        } else {
            console.log('No case row was found :( !', err);
        }
      })

Username is a variable where my username from form was inserted. I always get the error Unknown column 'username' in 'where clause' I have a register form and I want to check if a user already exists so there are no multiple users in the database, so that I can show an error if a user already exists.

You're missing quotes around the username so you're almost certainly getting an error. — Barmar
– Barmar, Commented Nov 16, 2021 at 9:01
Don't concatenate variables into the SQL. Use placeholders and a parameter array. — Barmar
– Barmar, Commented Nov 16, 2021 at 9:01
Assigning the username to the length (?) of another username doesn't sound like a useful operation to. You need to use placeholders as Barmar suggested. — CherryDT
– CherryDT, Commented Nov 16, 2021 at 9:03
@Barmar i am checkig the err i just forgot to put it in the post — anzeko
– anzeko, Commented Nov 16, 2021 at 9:04

Barmar · Accepted Answer · 2021-11-16 09:07:30Z

0

Don't substitute a variable into the SQL, use a placeholder and a parameter array.

 const selectUsername = conn.query("SELECT username FROM user WHERE username= ?", [username], function (err, row){

answered Nov 16, 2021 at 9:07

Barmar

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