Problems with elseif conditions - php

Question

I have a section of my code with a few elseif condtions that don't seem to be working properly. I've built a conditional drop down form that's working for the most part so far except for when it reach a couple elseifs.
I'm using JS to send the dropdown option name to my PHP script with GET which is where it seems to be going weird. For most of the form it pulls the options for the next dropdown from a MySQL query but for the first drop I've just used a few elseifs to make it less complex. you can check the live script here. Here's the section giving me trouble (it's the last two elseifs):
if (isset($_GET['setpoint'])) {
while ($row = mysql_fetch_array($result)) {
echo "<option value='" . $row{'stp'} . "'>" . $row{'stp'} . "</option>";
}
} elseif (isset($_GET['power'])) {
echo "<option>Please Choose Setpoint Options</option>";
while ($row = mysql_fetch_array($result)) {
$row{'stp'} = ucfirst($row{'stp'}); //capitalizes the first letter; necessary?
echo "<option value='" . $row{'stp'} . "'>" . $row{'stp'} . "</option>";
}
} elseif (isset($_GET['source'])) {
echo "<option>Please Choose Input Range</option>";
while ($row = mysql_fetch_array($result)) {
echo "<option value='" . $row{'sir'} . "'>" . $row{'sir'} . "</option>";
}
} elseif (isset($_GET['type']) && $_GET['type'] = "Digital") {
echo "<option>Please Choose Input Source</option>";
echo "<option value='RS232C'>RS232C</option><option value='RS422'>RS422</option><option value='RS485'>RS485</option><option value='current loop'>current loop</option>";
} elseif (isset($_GET['type']) && $_GET['type'] = "Analog") {
echo "<option>Please Choose Input Source</option>";
echo "<option value='DC current'>DC Current</option><option value='DC voltage'>DC Voltage</option><option value='AC current'>AC Current</option><option value='AC voltage'>AC Voltage</option><option value='process'>Process</option><option value='thermocouple'>Thermocouple</option><option value='RDT'>rdt</option>";
}
The first dropdown will set $_GET['type'] to either 'Analog' or 'Digital' but no matter which option $_GET['type'] is set to it will just run the first elseif that checks if $_GET['type'] is set. If $_GET['type'] = 'Analog' then it should be returning the last elseif and not the second to last.
This is most of the script for reference:
//prevents injections
//any order
isset($_GET['type'])?$type = urldecode($_GET['type']):"";
//$type = mysql_real_escape_string(urldecode($_GET['type']));
isset($_GET['source'])?$source = mysql_real_escape_string(urldecode($_GET['source'])):"";
isset($_GET['range'])?$power = mysql_real_escape_string(urldecode($_GET['range'])):"";
isset($_GET['setpoint'])?$setpoint = mysql_real_escape_string(urldecode($_GET['setpoint'])):"";
//forms the query depending on what data is recieved through GET
//first option on the bottom; last option on the top to avoid conflicts
if (isset($_GET['setpoint'])) {
$query = "SELECT DISTINCT stp FROM meters WHERE sio='$range' AND pso='$power' AND stp='$setpoint' ORDER BY model";
} elseif (isset($_GET['power'])) {
$query = "SELECT DISTINCT stp FROM meters WHERE sio='$range' AND pso='$power' ORDER BY model";
} elseif (isset($_GET['range'])) {
$query = "SELECT DISTINCT pso FROM meters WHERE sio='$range' ORDER BY model";
} elseif (isset($_GET['source'])) {
$query = "SELECT DISTINCT sir FROM meters WHERE sio LIKE '%$source%' ORDER BY sir";
}
//creates a result array from query results
isset($query)?$result = mysql_query($query):"";
//outputs dropdown options dependent on what GET variables are set
//first option on the bottom; last option on the top to avoid conflicts
if (isset($_GET['setpoint'])) {
while ($row = mysql_fetch_array($result)) {
echo "<option value='" . $row{'stp'} . "'>" . $row{'stp'} . "</option>";
}
} elseif (isset($_GET['power'])) {
echo "<option>Please Choose Setpoint Options</option>";
while ($row = mysql_fetch_array($result)) {
$row{'stp'} = ucfirst($row{'stp'}); //capitalizes the first letter; necessary?
echo "<option value='" . $row{'stp'} . "'>" . $row{'stp'} . "</option>";
}
} elseif (isset($_GET['source'])) {
echo "<option>Please Choose Input Range</option>";
while ($row = mysql_fetch_array($result)) {
echo "<option value='" . $row{'sir'} . "'>" . $row{'sir'} . "</option>";
}
} elseif (isset($_GET['type']) && $_GET['type'] = "Digital") {
echo "<option>Please Choose Input Source</option>";
echo "<option value='RS232C'>RS232C</option><option value='RS422'>RS422</option><option value='RS485'>RS485</option><option value='current loop'>current loop</option>";
} elseif (isset($_GET['type']) && $_GET['type'] = "Analog") {
echo "<option>Please Choose Input Source</option>";
echo "<option value='DC current'>DC Current</option><option value='DC voltage'>DC Voltage</option><option value='AC current'>AC Current</option><option value='AC voltage'>AC Voltage</option><option value='process'>Process</option><option value='thermocouple'>Thermocouple</option><option value='RDT'>rdt</option>";
Again, you can check the live script here.

Answer 1

$_GET['type'] = "Digital" is assignment, not a check.
What you need is
$_GET['type'] == "Digital"
Same with $_GET['type'] = "Analog"
It should be
$_GET['type'] == "Analog"
Also, like Darkbee mentioned, use PDO or MySQLi

Answer 2

You're assigning $_GET['type'] when I think you want the comparison operator equals:
$_GET['type'] = "Digital"
becomes
$_GET['type'] == "Digital"

Answer 3

try
elseif (isset($_GET['type']) && $_GET['type'] == "Digital")
and
elseif (isset($_GET['type']) && $_GET['type'] == "Analog")
Two Equal signs is an equal one is an assignment (will return true always)