如何根据$ variable值触发查询?

please excuse me if i am not stating this correctly or using correct terminology since i am new to php development.

I have a page called photos.php and i want to dos something like photos.php?type=me and photos.php?type=friends. As you can infer, with type=me i want to show my photos and with type=friends i want to display friends' photos. So i want to do something like:

if $value == $me trigger type=me query and if $value == $friends trigger query to 
display only friends' photos.

It's as simple as you wrote:

if ($_GET['type'] == 'me') {
    $sql = 'me query';
} else if ($_GET['type'] == 'friends') {
    $sql = 'friends query';
}

Queries depends on your database structure.

$query = ($_GET['type'] == 'me') ? 'me query' : (($_GET['type'] == 'friends') ? 'friends query');

that should do the trick