Please provide a reproducible test case, including SQL definitions and "the other statements" you mention, if they are needed for a minimum test case.

Thanks!

Here is the SQL definition:

CREATE TABLE test1 (
  c1 int(4) unsigned zerofill NOT NULL auto_increment,
  c2 varchar(10) default NULL,
  c3 double(4,2) default NULL,
  PRIMARY KEY  (c1)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8;

Code with problem:

// Opening connection
include ('../mysql/param.inc');
$db = new mysqli($hote, $util, $mpas, $base); 
if (!$db) {
	echo "No connection!";
	exit();
}
echo 'Non Prepared Request<br />';  //WORK WELL
$sql = "select * from test1"; 
$rqp = $db->query($sql); 
echo 'Rows = '.$rqp->num_rows.'<br />';

echo '<br />Prepared Request<br />'; //DON'T WORK
$sql = "select * from ch9books"; 
$rqp = $db->prepare($sql);
$rqp->execute();
echo 'Rows = '.$rqp->num_rows.'<br />';

// Closing connection 
$db->close();


And the results...


Non Prepared Request
Rows = 6

Prepared Request
Rows = 0

Stupid me, ... no bug, of course - wrong API usage. 

Prepared Statements work with unbuffered result sets by default. PS can't tell you how many rows there are in the result set before you either have:

 - stored the result set / turned it into a buffered result set
 - fetched all data

You have neither called mysqli_stmt_store_result() nor fetched all results before you call mysqli_stmt_num_rows(). Therefore, mysqli_stmt_num_rows() returns 0, which is correct.

http://www.php.net/manual/en/function.mysqli-stmt-num-rows.php

"Returns the number of rows in the result set. The use of mysqli_stmt_num_rows()  depends on whether or not you used mysqli_stmt_store_result() to buffer the entire result set in the statement handle.

If you use mysqli_stmt_store_result(), mysqli_stmt_num_rows() may be called immediately. "

See also http://dev.mysql.com/doc/refman/5.1/en/mysql-stmt-num-rows.html

Wrong usage of API, ext/mysqli acts as described in the manual