Does db_affected_rows() works well with PostgreSQL?

Question

This is a clean installation and I was starting to develop a module.
So I have the following code (and nothing more apart from the hook_menu()):

$result = db_query("SELECT * FROM {variable}");
return db_affected_rows();

I used the variable table as an example since it was likely to be populated (and it is, of course!). Well, to my surprise db_affected_rows() always returns 0.
Is there any reason why it doesn't work? Are there any reported bugs that I may have missed?

Setup:

• Drupal 6.22
• PostgreSQL 8.4
• PHP 5.3.8

Answer 1

To summarize for Drupal 6:

• db_affected_rows() gives you number of rows returned by a select if the database is MySQL but not if it's PostgreSQL.
• In Drupal 6 if you are using PostgreSQL you can run pg_num_rows() on the query to get the number of rows.

It is indeed database specific.

_{[Reference: this comment in the Drupal documentation]}