I'm trying to update my student records but it's not updating and there's no error.

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PHP

its always show that my query is not working. "Database Error: Unable to update record. i already try to print my query and show this

"UPDATE students set first_name = 'Alex', last_name = 'Rawr', year = '4', course = 'IT', subjects = 'sdd', WHERE id ='1' " the id is given. any tips about this.

$action = isset( $_POST['action'] ) ? $_POST['action'] : "";

if($action == "update"){

    $query = "UPDATE students

    set 

     first_name = '".$mysqli->real_escape_string($_POST['first_name'])."',

     last_name = '".$mysqli->real_escape_string($_POST['last_name'])."',

     year = '".$mysqli->real_escape_string($_POST['year'])."',

     course = '".$mysqli->real_escape_string($_POST['course'])."',

     subjects = '".$mysqli->real_escape_string($_POST['subjects'])."',

     WHERE id ='".$mysqli->real_escape_string($_REQUEST['id'])."' ";

        if($mysqli->query($query) ) {

        //if updating the record was successful

        echo "User was updated.";

        }else{

        //if unable to update new record

        echo "Database Error: Unable to update record.";

        }

}


$row = $result->fetch_assoc();

//assign the result to certain variable so our html form will be filled up with values
    $id         = $row['id'];
    $first_name = $row['first_name'];
    $last_name  = $row['last_name'];
    $year       = $row['year'];
    $course     = $row['course'];
    $subjects   = $row['subjects'];

<!--we have our html form here where new user information will be entered-->

<form action='#' method='post' border='0'>

<table>

<tr>

<td>Firstname</td>

<td><input type='text' name='first_name' value='<?php echo $first_name;  ?>' /></td>

</tr>

<tr>

<td>Lastname</td>

<td><input type='text' name='last_name' value='<?php echo $last_name;  ?>' /></td>

</tr>

<tr>

<td>Year</td>

<td><input type='text' name='year'  value='<?php echo $year;  ?>' /></td>

</tr>

<tr>

<td>Course</td>

<td><input type='text' name='course'  value='<?php echo $course;  ?>' /></td>

<tr>

<tr>

<td>Subjects</td>

<td><input type='text' name='subjects'  value='<?php echo $subjects;  ?>' /></td>

<tr>

<td></td>

<td>

<!-- so that we could identify what record is to be updated -->

<input type='hidden' name='id' value='<?php echo $id ?>' />

<!-- we will set the action to update -->

<input type='hidden' name='action' value='update' />

<input type='submit' value='Edit' />

<a href='displayRecords.php'>Back to display page</a>

</td>

</tr>