Is it possible to query a mySQL Database using Optgroup? - php

Question

For example, say I have the following code:
Choose a city:
<select name="city">
<optgroup label="East Coast Cities">
<option value="New York">New York</option>
<option value="Atlanta">Atlanta</option>
<option value="Miami">Miami</option>
</optgroup>
<optgroup label="West Coast Cities">
<option value="Las Vegas">Las Vegas</option>
<option value="Los Angeles">Los Angeles</option>
<option value="San Francisco">San Francisco</option>
</optgroup>
</select>
This will give me the correct drop down menu.. now.. say that each value is a also a value in my mySQL database. So for example, i have a table in my DB which also has these cities which is connected to a 900 row table with different people, each living in ONE of these cities.. What i would like to do is have it so that when someone selects a category it only searches for the people living in that city based on other specifications.. This is what I have in mind so far for the php file i'll use:
<?php $con=mysqli_connect("server","username","password","Database");
// Check connection
if (mysqli_connect_errno())
{
throw new Exception(mysqli_connect_error(), mysqli_connect_errno());
}
$city_query = $_POST['city'];
$result = mysqli_query($con,"SELECT name, address, city_name
FROM (People INNER JOIN City ON People.city_name = City.city_name)
WHERE city_name = $city_query");
//print out table using echo
mysqli_close($con); ?>
I hope this is fairly clear. Any help is appreciated, thank you.