cant update multiple existing rows in php mysql - php

Question

I have this edit form:
<?php
while($rows=mysql_fetch_array($query)){
$area=$rows['area'];
$dates=$rows['dates'];
$number_of_local_hires=$rows['number_of_local_hires'];
$salary_per_local_hire_per_day=$rows['salary_per_local_hire_per_day'];
$amount=$rows['amount'];
echo "<tr id='addr0'>";
echo "<td>";
echo "<input type='text' name='ca_salary_area[]' placeholder='Area' class='form-control' value='$area' required/>";
echo "</td>";
echo "<td>";
echo "<input type='text' name='ca_salary_date[]' placeholder='Date/s' class='form-control' value='$dates' required/>";
echo "</td>";
echo "<td>";
echo "<input type='text' name='ca_salary_localhires[]' placeholder='Number of Local Hires' class='form-control' value='$number_of_local_hires' required/>";
echo "</td>";
echo "<td>";
echo "<input type='text' name='ca_salary_perday[]' placeholder='Salary Per Local Hire Per Day' class='form-control' value='$salary_per_local_hire_per_day'required/>";
echo "</td>";
echo "<td>";
echo "<input type='text' name='ca_salary_amount[]' placeholder='Amount' class='form-control' value='$amount'/>";
echo "</td>";
echo "</tr>";
}
?>
But I can't update it using this query in my edit_salary.php:
$sql_rows = mysql_query("SELECT *FROM `tblcasalaryformdetails` WHERE casalaryform_id =$id");
$num_rows = mysql_num_rows($sql_rows);
if ($num_rows == count($_POST['ca_salary_area'])){
for($i=0;$i<$num_rows;$i++)
{
$nos_hire = $_POST['ca_salary_localhires'][$i];
$nos_salaray = $_POST['ca_salary_perday'][$i];
$subtotal_salary_amount = $nos_hire * $nos_salaray;
$sql = "UPDATE `tblcasalaryformdetails`
SET area = '". $_POST['ca_salary_area'][$i]."',
dates = ". $_POST['ca_salary_date'][$i].",
number_of_local_hires = ". $_POST['ca_salary_localhires'][$i].",
salary_per_local_hire_per_day = ". $_POST['ca_salary_perday'][$i].",
amount = ". $subtotal_salary_amount."
WHERE casalaryform_id = $id";
mysql_query($sql);
}
}
The result is all the values will be updated same as the last row value. What did I missed? I tried show its index, it looks fine.