<?php
$servername = ""; $username = ""; $password = ""; $dbname = "";
$conn = mysqli_connect($servername, $username, $password, $dbname);
if (!$conn) {
die("Connection failed: " . mysqli_connect_error());}
$sql_1 = "SELECT id, title, main_image FROM posts WHERE $sql_2 = 'category_title' AND $sql_3 ='country_iso_code'";
$sql_2 = "SELECT id, post_id, category_title FROM post_categories";
$sql_3 = "SELECT id, post_id, country_iso_code FROM post_countries";
$category_title =$_REQUEST['category'];
$country_iso_code =$_REQUEST['country'];
$result = mysqli_query($conn, $sql_1);
if (mysqli_num_rows($result) > 0) {
// output data of each row
while($row = mysqli_fetch_assoc($result)) {
    echo "id: " . $row["id"]. " - Title: " . $row["title"]. " " .         $row["main_image"]. "<br>";
}
} else {
echo "0 results";
}

mysqli_close($conn);
?>