无法比较两个PHP变量

$var1 = 123;
$var2 = "123";

if ($var1 == $var2) {
    echo "变量相等";
} else {
    echo "变量不相等";
}

$var1 = 123;
$var2 = "123";

if ($var1 === $var2) {
    echo "变量相等";
} else {
    echo "变量不相等";
}

$var1 = 123;
$var2 = "123";

if (strval($var1) === strval($var2)) {
    echo "变量相等";
} else {
    echo "变量不相等";
}