Retrieves the number of rows from a result set. This command is only valid for statements like SELECT or SHOW that return an actual result set. To retrieve the number of rows affected by a INSERT, UPDATE, REPLACE or DELETE query, use mysql_affected_rows().
The result resource that is being evaluated. This result comes from a call to mysql_query().
Note: If you use mysql_unbuffered_query(), mysql_num_rows() will not return the correct value until all the rows in the result set have been retrieved.
Note: For downward compatibility, the following deprecated alias may be used: mysql_numrows()