PHP删除功能失败，没有错误

In the top of my admin PHP (admin.php), I have loaded data from "Sport" table in "DogSport" MySQL database. After clicking "Edit" link of a particular record, I can edit, delete that record on "editform2.php". Even on that page, I can also insert a new record.

Problem: Deleting first and second records do not work! Deleting all following records work fine. This problem only with deleting functionality.

admin.php

I have uploaded necessary files, you can also use to check it including database .sql script. Your help is appreciated.

https://www.dropbox.com/s/wn40u93oa1sxcph/SO.rar?dl=0

Code segment - admin.php

include("dbconnect.inc.php");
//Retrieving Data
$query1 = "SELECT * FROM Sport ORDER BY SportId ASC";
$result2 = mysqli_query($con, $query1);
$rows = mysqli_num_rows($result2);
$i = 0;
if ($rows == 0)
    echo "<br/>There are no records";
else {
    echo "<table id='sport'>";
    echo "<tr><th>Sport Id</th><th>Sport Name</th><th>Description</th></tr>";

    while ($row = mysqli_fetch_array($result2)) {
        echo "<tr><td>" . $row["SportId"] . "</td><td>" . $row["SportName"] . "</td><td>" . $row["Description"] .
        "</td><td> <a href='editform2.php?id=" . $row["SportId"] . "' target='_blank'>Edit</a></td></tr>";

        $i++;
    }
    echo "</table>";
}

Code segment - editform2.php

if (isset($_POST["delete"])) {
    $id = $_GET["id"];
    include("dbconnect.inc.php");
    $query3 = "DELETE FROM Sport WHERE SportId=$id";
    mysqli_query($con, $query3);
    echo "<h1>Deleted Successfully</h1>";
    mysqli_close($con);
}

UPDATE!!!! I get this error now

DogSport is in use.Error: DELETE FROM Sport WHERE SportId=2 Cannot delete or update a parent row: a foreign key constraint fails (dogsport.orders, CONSTRAINT orders_ibfk_1 FOREIGN KEY (EqId) REFERENCES equipment (EqId))