var sql = require('mysql');
var db_config = {
  host: 'localhost',
  user: 'root',
  password: 'uttkarsh',
  database: 'partners_invoice'
}
var connection = sql.createConnection(db_config);
// connection.connect(...) is just a way to test whether database connection
// is working or not. I'm not sure about it's return value.
// You need to use that connection object for queries.
//
//var con = connection.connect(function(err){
//  if(err) throw err;
//})

// User_ID is not defined :
var User_ID=1234;
connection.query('SELECT * FROM user_data WHERE User_ID = ?',[User_ID], function(error, result){
  if(error) throw error;
  console.log(result);
});
connection.end();