pset7: understanding php arrays

Question

I'm having a lot of trouble understanding these arrays in php. Here I want to query SQL to get me the value of cash of the user. Then I want to add it to the $position variable that is later sent to the view. I'v tried a lot now, but i get the error message: Notice: Undefined index: cash

// configuration
require("../includes/config.php"); 
$id = $_SESSION["id"];
$rows = query("SELECT * FROM `stocks` WHERE $id");
$cash = query("SELECT cash FROM `users` WHERE id = ?", $_SESSION["id"]);
print_r(array_values($cash));
print_r(array_values($rows));

$positions = [];
       $positions[] = ["cash" => $cash["cash"]];

foreach ($rows as $row)
{
    $stock = lookup($row["symbol"]);
    if ($stock !== false)
    {
        $positions[] = [
            "name" => $stock["name"],
            "price" => $stock["price"],
            "shares" => $row["shares"],
            "symbol" => $row["symbol"],
        ];
    }
}
render("portfolio.php", ["positions" => $positions, "title" => "Portfolio"]);

Answer 1

First, after WHERE you should specify column name(s). So this call to query()

$rows = query("SELECT * FROM `stocks` WHERE $id");

should be like that

$rows = query("SELECT * FROM stocks WHERE columnName = ?", $id);

Second, the function query() returns a number of rows, at the first place, where each row is composed of columns. Meanwhile, if you tried to dump() the variable named $cash, you'd find that it's a multi-dimensional array. In order to access the index named cash, you should do something like

$cash[0]["cash"] // access the index named cash in the first row (row[0])

So instead of

$positions[] = ["cash" => $cash["cash"]];

Probably you should have

$positions[] = ["cash" => $cash[0]["cash"]];

Hope that helps!