Normally SQL is not read from file like you have setup. If sql does come from a file it is commonly just the statements to execute but not the connector prepared statements or execution.
If you need to read from a file you would typically do something like:[LIST=1]
[*]read sql statements from file into a variable, say $sql;
[*]next, use this in your php page.
$sql = file_get_contents(select_companies.sql);
$stmt = $o_Db->prepare($sql);
$result = $stmt->execute();
Your select_companies.sql might look like:
This is a bit of a shot in the dark as you did not show any of your files that you read from or the code that you are using.