Select query depends on many possibilities

I have 4 Select in HTML users, industry, lead_source and country. These selects have default value which is equal to select.

I want to make a query to select row from table leads where the only selected values.

This is the html code:

<select class="form-control" name="lead_source">
       <option value="select">-SELECT-</option>
       @foreach($leadssource as $leadsource)
               <option value=""></option>
       @endforeach
 </select>

<select class="form-control" name="industry">
    <option value="select">-SELECT-</option>
    @foreach($industries as $industry)
        <option value=""></option>
    @endforeach
</select>

<select class="form-control" name="user">
    <option value="select">-SELECT-</option>
    @foreach($users as $user)
        <option value=""></option>
    @endforeach
</select>

<select class="form-control" name="country">
    <option value="select">-SELECT-</option>
    @foreach($countries as $country)
        <option value=""></option>
    @endforeach
</select>

I want to select only the values which is not equal to first option which is select.

I have tried:

To use if statements and check all the available possibilities but it is not good because if I added one more option then I have to add more bunch of if statements.

Here is a example of my first if statement if all options is selected:

if($leadSource != 'select' && $industry != 'select' && $user != 'select' && $country != 'select'){
    $leads = Main::where('lead_source', '=', $leadSource)
                -> where('industry', '=', $industry) -> where('country', '=', $country) -> where('user', '=', $user) -> paginate(50);


    return view('filter.show') -> withLeads($leads);
}

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