PHP to execute PHP on another server and get the result

Yes it's possible. However, you need to make a JSON API: the server wich serve postgresql needs to fetch results from Database, then encode it in json with json_encode() method and return it with echo.

Then, you need to make an HTTP request from your shared hosting using CURL, here's an example:

function GetContent($url) {
    $curl = curl_init();
    $ua   = "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36";
    curl_setopt($curl, CURLOPT_URL, $url);
    curl_setopt($curl ,CURLOPT_USERAGENT, $ua);
    curl_setopt($curl, CURLOPT_COOKIESESSION, true);
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($curl, CURLOPT_FOLLOWLOCATION, true);
    $return = curl_exec($curl);
    curl_close($curl);
    return $return;
}

Then, call the function:

$sql = json_decode(GetContent('http://urlofyourserver/testJSON.php'));

You can now get the result in the $sql variable :)

Oh and don't forget, make a password request using $_GET requests on your server wich serves postgresql, otherwise everyone will be able to access to data if they found your server URL.

e.g: http://urlofyourserver/testJSON.php?secret=xxx

You can also pass the query as a get parameter, but It can be risked if your password is cracked.

Postgresql server sample

$realPass = "blablah";
if(isset($_GET['secret'])) {
   $pass = $_GET['secret'];
   if($pass === $realPass) {
     header('Content-type: application/json');
     // do query here and return it as $test var
     echo json_encode($test);

   }
}

You could use php curl

Example that will send the get parameters get1 and get2 to a test.php on a server with IP 192.168.2.2

// Get cURL resource
$curl = curl_init();

// Set some options - we are passing in a useragent too here
curl_setopt_array($curl, array(
    CURLOPT_RETURNTRANSFER => 1,
    CURLOPT_URL => 'http://192.168.2.2/test.php?get1=value&get2=value2',
    CURLOPT_USERAGENT => 'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)'
));

// Send the request & save response
// The response could be JSON with the results from the database
$resp = curl_exec($curl);

// Close request to clear up some resources
curl_close($curl);

You could use PHP to encode and decode your results in JSON to make things easier. To do this use json_encode() and json_decode()

If you want some more information check out:

• http://codular.com/curl-with-php
• http://php.net/manual/en/curl.examples.php
• http://php.net/manual/en/curl.examples-basic.php

I just came up with another idea that is much better imho; it also might be better in terms of security.

use a PHP script that simulates being an image file:

// example code for getting binary image data from db 
// (PDO and MySQL in this example)

$stmt = $pdo->prepare( "SELECT image_bin FROM image_table WHERE id = :id LIMIT 1" );
$stmt->bindValue(":id", $_GET["id"], PDO::PARAM_INT);
$stmt->execute();
$image_bin = $stmt->fetchColumn();

header('Content-Type: image/png');
echo $image_bin;

on the page where you want to show the image you don't even need to use PHP:

<img src="http://myimageserver.com/image.php?id=3425">

in this example you just need to use the GET variable id to define/decide which image is shown. most of the work is done on the remote server where you could grab the desired image by using POSTGRESQL like you mentioned.