mysqli_statement :: num_rows（）返回错误的值

Question

I was writing a database handler class in PHP using the mysqli class and prepared statements. I was attempting to print out the result. It didn't work right off the bat so I decided to do some debugging. I tried to use the num_rows() method from the mysqli_statement class, but it kept returning 0. I decided to write a small portion of test code to keep it simpler so I could see what was going wrong. I was then able to return the data I wanted, but the num_rows() method still returns 0 even when it is actually selecting and retrieving some data. Here is the code:

$mysqli = new mysqli('localhost', 'username', 'password', 'database');
if(mysqli_connect_errno())
{
  die('connection failed');
}

$statement = $mysqli->stmt_init();

$query = "SELECT name FROM table WHERE id = '2000'";
if($statement->prepare($query))
{
    $statement->execute();
    $statement->bind_result($name);
    $statement->fetch();
    $statement->store_result();
    echo $statement->num_rows();
    echo $name; 
}
else
{
    echo 'prepare statement failed';
    exit();
}

So yeah, expected result is:

1name

And actual result is:

0name

Can anyone tell me why this is?

Answer 1

I wonder if num_rows() is reporting relative to the current resultset. Try capturing num_rows() prior to fetching the data. e.g.

if($statement->prepare($query))
{
    $statement->execute();
    $statement->store_result();
    echo $statement->num_rows();
    $statement->bind_result($name);
    $statement->fetch();
    echo $name; 
}

Does that have any effect?