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Editorial Team
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Asked: 2026-06-03T11:06:48+00:00

For example I have the following MySQL table: parent_id | child_id ——————— 1 |

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For example I have the following MySQL table:

parent_id | child_id
---------------------
       1  |  4
       1  |  3
       1  |  5
       2  |  8
       3  |  7

I want to print out the parent and all its children in a format like below:

parent     |    child
---------------------
           |      4
        1  |      3
           |      5
---------------------
        2  |      8
---------------------
        3  |      7

Basically I just want to display the parent ONCE(Distinct) and list out all its children with PHP. Is it possible to retrieve the above result with just ONE SQL query? I can get the above result if I first query the parents and then recursively query the children using the parent ids but that would be alot more SQL queries hitting the DB.

Or, do I retrieve the result containing every parent_id & children_id and achieve the above result in PHP by using arrays. If so, please tell me how.

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1 Answer

  1. Editorial Team

    Yes. Select normally and use the parents as keys in an array.

    //Query normally
while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
    $result[$row["parent_id"]][] = $row["child_id"];
}

    Or something similar.

    EDIT

    The display part would look something like this:

    <?php

$result = array(
    1 => array(4, 3, 5),
    2 => array(8),
    3 => array(7)
); //Assuming you get a resultset like this.
$rowIsOpened = false; //Indicates whether a row is currently opened.

//I'm using $rowIsOpened because the row immediately after the rowspanned cell shouldn't be closed.

echo <<<HTML
<table>
    <thead>
        <tr>
            <th>Parent</th>
            <th>Children</th>
        </tr>
    </thead>
    <tbody>
HTML;
//Echo a bunch of HTML before actually looping

foreach ($result as $parent => $children) {
    echo "<tr>";
    echo "<td rowspan=";
    echo count($children); //Span over <how many children are> rows
    echo ">$parent</td>";
    $rowIsOpened = true; //Row is opened
    foreach ($children as $child) {
        if (!$rowIsOpened) {
            echo "<tr>";
        } //Only open a row if row is not opened
        echo "<td>$child</td>";
        echo "</tr>";
        $rowIsOpened = false; //Row is now closed. Ready for next iteration.
    }

}
//Close the table tags etc.
echo <<<HTML
    </tbody>
</table>
HTML;
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