<?php
$data = array(array(
	"transaction_no" => 123,
	"transaction_date" => "Old value"));

echo "Before Update loop\n-------------------------------\n";
echo "<pre>";
print_r($data);
foreach($data as $key => $value)
{
  $data[$key]['transaction_date'] = "New Value";
}
echo "After Update loop\n----------------------------\n";
echo "<pre>";
print_r($data);

Before Update loop
-------------------------------
<pre>Array
(
    [0] => Array
        (
            [transaction_no] => 123
            [transaction_date] => Old value
        )

)
After Update loop
----------------------------
<pre>Array
(
    [0] => Array
        (
            [transaction_no] => 123
            [transaction_date] => New Value
        )

)