Log File With Changes Made to MySQL DB - php

Question

I would like to create a .txt log file that records changes made to a database. Basically whenever someone adds a record, I want the log to record something like "On 2013-10-03 12:21:43 Smith, Joe added the following appointment: ...some appointment details..."
I have a functions.php file that has the following function (oh, and bear with me for the moment on mysql vs mysqli - that update is in the works, but hasn't happened yet):
function getCalendarChange($id) {
require("db.php"); //database connection
$sql = "SELECT calendar_event.consultant_id, calendar_event.client_id, calendar_event.event_id, calendar_event.billing_id, calendar_event.dates_id, consultant.f_name, consultant.l_name, client.client_name, event_type.event_type, billing_status.billing_type, dates.date FROM calendar_event
INNER JOIN consultant ON calendar_event.consultant_id = consultant.consultant_id
INNER JOIN client ON calendar_event.client_id = client.client_id
INNER JOIN event_type ON calendar_event.event_id = event_type.event_id
INNER JOIN billing_status ON calendar_event.billing_id = billing_status.billing_id
INNER JOIN dates ON calendar_event.dates_id = dates.date_id
WHERE calendar_event_id = '$id'";
$result = mysql_query($sql,$connection) or die (mysql_error());
$results = mysql_fetch_array($result);
$consultant = $results['l_name'] . ", " . $results['f_name'];
$client = $results['client_name'];
$event = $results['event_type'];
$billing = $results['billing_type'];
$eventdate = $results['date'];
echo $consultant . " " . $client . " " . $event . " " . $billing . " " . $eventdate;
}
In the page that processes the form to INSERT a new record, I have the following:
include("functions.php");
$add_appt_query = "INSERT INTO calendar_event (calendar_event_id, consultant_id, client_id, event_id, billing_id, dates_id) VALUES (NULL, '$addee', '$addclient', '$addevent', '$addbilling', '$dt')";
$add_appt_result = mysql_query($add_appt_query,$connection) or die(mysql_error());
$chngid = mysql_insert_id(); //gets the last auto increment id - yes this is set to be an auto increment column
$new_appointment = "<p>Appointments added successfully.</p>"; //everything works up to here - the appointment is added to the db as expected
// start log new appointment
$log_data = "On " . $log_datetime . " " . $ee_log_name . " added the following appointment: "; //$log_datetime and $ee_log_name are defined elsewhere, but work correctly
$log_data .= getCalendarChange($chngid) . "\n";
$log_data .= file_get_contents('mod.txt');
file_put_contents('mod.txt', $log_data); //done this way so the newest change is at the beginning of the file not the end
// end log new appointment
What ends up in mod.txt is something like "On 2013-10-03 12:21:43 Smith, Joe added the following appointment: " it adds everything I want except for the data from getCalendarChange().
I have tried to remove getCalendarChange and just echo $chngid, which produces the id# as you might expect.
I have called the getCalendarChange function with a static number getCalendarChange(100) from within the functions.php file, which displays the correct information for that particular event.
I have replaced $chngid in getCalendarChange($chngid) to getCalendarChange(100), and it still doesn't work. (yes there is a record with id 100).
Why doesn't getCalendarChange($chngid) work outside of the functions.php file?