How do I get the total number of rows returned by a MySQL query

I want to know the total number of rows being returned by the following query

				$sql = "SELECT *
					FROM " . ADR_LIBRARY_TABLE ."
					WHERE book_difficulty <= $book_difficulty 
					AND book_zone = $area_id";
				$result = $db->sql_query($sql);
				if( !$result )
				{
					message_die(GENERAL_ERROR, 'Could not obtain book information', "", __LINE__, __FILE__, $sql);
				}
				$library = $db->sql_fetchrow($result);

PHP:

I thought that

mysql_num_rows($library);

PHP:

would return this, but it causes an error

mysql_num_rows(): supplied argument is not a valid MySQL result resource

Code (markup):

 

Never mind, think I see what I was doing wrong. Should have used this instead

mysql_num_rows($result);

PHP:

 

Slightly different problem now

				$sql = "SELECT *
					FROM " . ADR_LIBRARY_TABLE ."
					WHERE book_difficulty <= $book_difficulty 
					AND book_zone = $area_id";
				$result = $db->sql_query($sql);
				if( !$result )
				{
					message_die(GENERAL_ERROR, 'Could not obtain book information', "", __LINE__, __FILE__, $sql);
				}
				$books = mysql_num_rows($result);
				$library = $db->sql_fetchrow($result);
			}

			if ( !$library )
			{
				adr_previous ( Adr_library_failure , adr_research , '' );
			}
			else
			{
				// Now roll for research
				$rnd_research = mt_rand ( 1 , $books);

				$sql = "SELECT *
					FROM " . ADR_LIBRARY_TABLE ."
					WHERE book_id = '".$library[$rnd_research]['book_id']."' ";
				$result = $db->sql_query($sql);
				if( !$result )
				{
					message_die(GENERAL_ERROR, 'Could not obtain book information', "", __LINE__, __FILE__, $sql);
				}
				$research_result = $db->sql_fetchrow($result);

PHP:

The above code is supposed to get all possible results for a MySQL query and store them as $library. Then, a random result is called from this list, and all it's information retrieved from the database. The first query works, the second doesn't.

 

do you have any errors ? or script doesn't reach that ELSE?
did you check $library value?

 

No errors. By echo statements, I've found that $library[$rnd_research]['book_id'] has no value. It's supposed to get a random row from $library, as determined by $rnd_research. However, it doesn't. $library['book_id'] has a value, but always the same one.

 

Found what was wrong

This

$library = $db->sql_fetchrow($result);

PHP:

should have been

$library = $db->sql_fetchrowset($result);

PHP: