PHP: Inserting foreign keys into sql DB - php

Question

I have three tables: GPs, patients and appointments. The IDs for GPs and patients are also foreign keys in the appointments database. I am creating an insert form for the appointments table, but cant seem to get it to work. It gives the following error: "Unknown column 'date' in 'field list' ".
GP table cols:
GPID,
first_name,
last_name,
surgery_name,
surgery_address,
GP_photo
patient table cols:
PID,
first_name,
last_name,
address,
phone,
P_photo
my php:
<?php
include("includes/connect.php");
if (isset($_POST['submit'])) {
$gp = $_POST['GP'];
$patient = $_POST['patient'];
$date = $_POST['date'];
$time = $_POST['time'];
$outcome = $_POST['outcome'];
if ($date == '' or $time == '' or $outcome == '') {
echo "<script>alert('One or more of your fields are blank, "
. "please ensure you have entered content in ALL fields.')</script>";
} else {
$insert_query = "insert into appointments (GPID,PID,date,time,outcome)"
. " values('$gp','$patient','$date','$time','$outcome')";
mysql_query($insert_query);
}
}
?>
My form:
<form action="appointments.php" method="post">
<table>
<tr>
<td>GP:</td>
<td><select name="GP">
<?php
include("includes/connect.php");
$GP_list = mysql_query("SELECT GPID, first_name, last_name FROM GPs");
while ($row = mysql_fetch_array($GP_list)) {
echo'<option value="' . $row['GPID'] . '">' . $row['GPID'] .
': ' . $row['first_name'] . ' ' . $row['last_name'] .
'</option>';
}
?>
</select>
</td>
</tr>
<tr>
<td>Patient:</td>
<td><select name="patient">
<?php
include("includes/connect.php");
$P_list = mysql_query("SELECT PID, first_name, last_name FROM patients");
while ($row = mysql_fetch_array($P_list)) {
echo'<option value="' . $row['PID'] . '">' . $row['PID'] .
': ' . $row['first_name'] . ' ' . $row['last_name'] .
'</option>';
}
?>
</select>
</td>
</tr>
<tr>
<td>Date:</td>
<td><input type="date" name="date"></td>
</tr>
<tr>
<td>Time:</td>
<td><input type="time" name="time"></td>
</tr>
<tr>
<td>Outcome:</td>
<td><textarea rows="8" cols="40" name="outcome"></textarea>
<input type="submit" name="submit" value="Book appointment"></td>
</tr>
</table>
</form>