多个关键字/条件搜索(AND,OR,无值输入标记)PHP MySQL

I'm beginner in PHP MySQL. It's gonna be too long to explain, I having much not likely error but something error in conditions. I found that trigger the problem, I found that it's more likely in AND, OR, Input tag no value.

Scenario
I have a search form with multiple inputs. Let's pretend this is the search form, I can't send image due to low reputation.

G-Number: [________] (This is Unique key in my database)
Name: [__________]
Virtual Number: [__________]
[Search button]


Using OR condition
Let's pretend that I input 123456 in G-Number will query like this:

________________________________________
|   G-Number   |     Name      |     Virtual Number    |
----------------------------------------------------------------
|   123456       |     John        |          001abc           |

So if only input John in Name, and 123456 in G-Number. The error here it shows all John even I input 123456 in G number.
Sample Result like this

GNumber | Name | Virtual Number
 123456   | John    | 001abc
 535243  | John    | 002efg
 965235  | John    | 002efg

Using AND condition

Here I need to fill up all the search form so it can search it, If I leave a blank it will say base from my system that No result Found
Basically if I input only 123456 in G-Number and leave the input blanks it can't search result so it's look like the code is this in SQL query

SELECT * FROM `subscribers` WHERE `fName` = '' AND `gNumber` = '123456' AND `virtualNumber` = '';

So basically the value of leave input form was space or like this ''.

That's why I'm looking for help and tips what should I do here, I don't want to use **MySQLi** and **PDO** now. I'm still practicing **MySQL**. All I want here function multiple keyword search.

Here is my codes:

**HTML FORM**
         <form class="form-inline" role="form" method="GET"  id="searchform">
          <div class="form-group">

          <input type="text" class="form-control" name="gnumber" placeholder="Number" style="margin-right: 2em;" >
          <input type="text" class="form-control" name="name"  placeholder="Input First or Last Name" style="width: 300px;margin-right: 2em;">
          <input type="text" class="form-control" name="virtual"  placeholder="Virtual Number" style="margin-right: 2em;">


          <br/><h5 style="float:right;"><button type="submit" class="btn btn-theme02" name="search" ><i class="fa fa-check">Search</i></button></h5>

          </div>

**THE PHP CODE**
  if (isset($_GET['search'])) {

        $gnum = htmlentities(mysql_real_escape_string($_GET['gnumber']));
        $name = htmlentities(mysql_real_escape_string($_GET['name']));
        $vr = htmlentities(mysql_real_escape_string($_GET['virtual']));



        if (empty($globe) && empty($name) && empty($vr)) {
         echo "<script> alert('Please select atleast 1 filter!')</script>";  
         exit;
        } else {
       $sql =  "SELECT * FROM `subscribers` WHERE `fName` = '".$name."' OR `gNumber` =  '".$gnum."' OR `virtualNumber` = '".$vr."'    ";
        }

      if ($result=mysql_query($sql)) {
          $query_num_rows = mysql_num_rows($result);
             if($query_num_rows == 0){ 
                echo "<script> alert('No Records Found!')</script>"; 

      } else {

       while($row=mysql_fetch_array($result)){
      // echo of result table is here.

Thank you.

$sql = "SELECT * FROM subscribers WHERE";

        if (empty($globe) && empty($name) && empty($vr)) {
         echo "<script> alert('Please select atleast 1 filter!')</script>";  
         exit;
        } 
        if(!empty($name)){
            $sql .append(`fName` = '".$name."'); 
        } 
        if(!empty($gnum)){
                  $sql .append(`gNumber` = '".$gum."');
        }

You have to follow such type of approach. I really do not know the Php syntax. But approach should be like this.