1. "Table" is a special term. Escape table name with `quotes`
2. $_GET['id'] is not escaped. This query can be injected.
3. $_GET['id'] is PHP, therefore it cannot be part of the SQL query string unless you concatenate it:

$query = "SELECT * FROM `table` WHERE id = " . $_GET['id'];

Thanks Cosmit for that detailed, yet easy to follow answer!

Cosmit's comment about SQL injection should not be taken lightly, as you're leaving yourself wide open here. I strongly recommend that you use PDO:
PHP: PDO - Manual

Get to the point where you understand the humor/horror of this:

Fair enough.