In Drupal 7, do database queries need to be enclosed by double quotes? I am migrating custom modules from Drupal 6 to 7. Since the database API changed it's quite a lot to do. During this I stumbled upon a problem regarding quotes. I am used to enclose strings in PHP with single quotes, so in Drupal 6 I wrote

$q = 'SELECT * FROM {node} WHERE type = "page"';

However, without any pattern (as far as I could detect) some of these queries fail in Drupal 7. When changing the above line to 

$q = "SELECT * FROM {node} WHERE type = 'page'";

it suddenly works. But I couldn't find any information if this quoting style is required by the new DAL. Anybody got further information on that or can confirm my observation?
Some SQL database engines are not supporting double quotes inside the query, that's why it didn't work out for you. Read more here: db_query#comment-11959.