<?php

function get_single ($select, $from, $where, $what)
{
    global $pdo;

    $stmt = $pdo->prepare("SELECT ".$select." FROM ".$from." WHERE ".$where." = ?");
    $stmt->execute([$what]);
    $value = $stmt->fetchColumn();

    echo $value;
}
get_single('nickname', 'user', 'id', 1);

?>