PHP表单验证没有按预期工作

i have wrote couple of lines of PHP code to make sure that form elements are not going to be empty anyhow.the algorithm was if the form field was not empty,it would echo out Okay" and if the form filed was kept empty it would echo out "not okay".but the problem is,every time time i submit that form despite keeping it not filled properly,it still outputs "Okay". i have checked the code but couldn't find any problem.here is my code given bellow,please have a look if you find any errors and let me know:

    <?php
if(isset($_GET['day']) && isset($_GET['date']) && isset($_GET['year'])){
    $day=isset($_GET['day']);
    $date=isset($_GET['date']);
    $year=isset($_GET['year']);
    if( !empty($day) && !empty($date) && !empty($year) ){
        echo "okay";
    }else{
        echo "please fill";
    }
}

?>
<form action="herok.php" method="GET">
    Day:<br><input type="text" name="day" /><br>
    Date:<br><input type="text" name="date" /><br>
    Year:<br><input type="text" name="year" /><br>
    <input type="submit" value="submit" />
</form>

A variable can be set but still be empty. Try checking for empty instead of isset

http://php.net/manual/en/function.empty.php

Please try this:

<?php
if(isset($_GET['day']) && isset($_GET['date']) && isset($_GET['year'])){
    $day=!empty($_GET['day']) ? $_GET['day'] : '' ;
    $date=!empty($_GET['date']) ? $_GET['date'] : '' ;
    $year=!empty($_GET['year']) ? $_GET['year'] : '' ;
    if( !empty($day) && !empty($date) && !empty($year) ){
      echo "okay";
    } else{
      echo "please fill";
    }
}

?>

Remove isset inside the if statement block:

<?php
if(isset($_GET['day']) && isset($_GET['date']) && isset($_GET['year'])){
    $day=$_GET['day'];
    $date=$_GET['date'];
    $year=$_GET['year'];
    if( !empty($day) && !empty($date) && !empty($year) ){
        echo "okay";
    }else{
        echo "please fill";
    }
}else{
    echo "please fill";
}

how make it more simple like this.

 $vars = array('day','date','year');
    $cecked = true;
    foreach($vars as $v) {
       if (!isset($_GET[$v]) || empty($_GET[$v])) {
            $cecked = false;
      }
    }
    if (!$cecked) {
    echo "please fill all require data";
    exit();

    } else {
echo "oke";
}