MySQL PHP将两行数据插入多维数组

Question

I am trying to insert data into a multidimensional array from two tables in my database, but it does something that I don't really know how to fix.

First of all, here is my PHP script:

if ($stmt = $mysqli->prepare('SELECT objects_price.object_id, materials.material_id, materials.name, material_amount
                              FROM objects_price
                              INNER JOIN materials ON objects_price.material_id=materials.material_id
                             ')) {
    $stmt->execute();

    $stmt->bind_result($object_id, $material_id, $material_name, $material_amount);
    $j = 1;
    $arr = array();

    while ($stmt->fetch()) {
        $k = 1;
        if ($object_id == $k) {
            $arr[] = array($j, $material_name, $material_amount);
            $k++;
            $j++;
        }
    }

    $stmt->close();

This script takes out some values from the database and inserts them in the array. My database looks like this: (objects_price)

(materials)

What happens right now is that it only outputs:

If I change the database query to:

if ($stmt = $mysqli->prepare('SELECT objects_price.object_id, materials.material_id, materials.name, material_amount
                            FROM objects_price
                            INNER JOIN materials
                            ')) {

it outputs this:

So the left side of this table is shown correct, but the right side shows only the first row of the price, (47). It should look like this:

I don't know if this is easily achieveable by changing the database query. But I hope I can get some advice, suggestions or help in here. Thanks in advance.

Answer 1

Try using a left join for your table:

$query = "SELECT m.name, op.objects_id
    FROM objects_price op 
    LEFT JOIN materials m USING(material_id)";
$result = $mysqli->query($query);

The next thing you need to change is the way you handle the results. It's quite possible you're going through the results and skipping many, which is why you only end up with one. Try this:

$arr = array();
while($row = $result->fetch_assoc()) {
    $arr[$row['objects_id']] = $row['name'];
}

If you have more than 1 material per object then just use this slight adjustment for a multidimensional array

$arr = array();
while($row = $result->fetch_assoc()) {
    $arr[$row['name']][] = $row['objects_id'];
}

Then to produce your table from this:

echo '<table>';
foreach($arr as $name => $objects) {
    echo '<tr><td>' . $name . '</td><td>';
    $space = '';
    foreach($objects as $id) {
        echo $space . $id;
        $space = ", ";
    }
    echo '</td></tr>';
}
echo '</table>';

A few tips:

1. if you're not putting any variables in, you don't need to prepare the query. You can just run it as above.
2. Don't select more columns than you need. Why grab all columns from the table when you only use 2?
3. if you're joining on a column that has the same name in both tables you can use USING(column_name) .

Answer 2

Everything looks good in your code except for these lines:

 while ($stmt->fetch()) {
    $k = 1;

What is happening is that $k is being declared and given the value of 1. Because it is in the loop, each time that line is run the value goes back to 1. To solve this simply put that value outside the loop like this:

 $k = 1;
 while ($stmt->fetch()) {
     //blah blah blah
 }