Why Does `mysqli_num_rows()` Return 0 After `mysqli_stmt::execute()`?

Why mysqli_num_rows() Returns 0 in PHP

In MySQLi, executing queries without first fetching results can lead to incorrect row counts. When encountering this issue with mysqli_num_rows(), consider the following:

Code Sample and Explanation

Consider the code snippet below:

$mysqli->prepare("SELECT id, title, visible, parent_id FROM content WHERE parent_id=? ORDER BY page_order ASC;");
$stmt->bind_param('s', $data->id);
$stmt->execute();

$num_of_rows = $stmt->num_rows; // Error!

$stmt->bind_result($child_id, $child_title, $child_visible, $child_parent);

while ($stmt->fetch()) {
  //...
}

echo($num_of_rows);

In this code, mysqli_num_rows() always returns 0 because the results haven't been fetched yet.

Solution: Use mysqli_stmt::store_result()

Prior to calling mysqli_num_rows(), you need to call mysqli_stmt::store_result() to store the query results in a buffer. This process enables rowCount counting:

$mysqli->prepare("SELECT id, title, visible, parent_id FROM content WHERE parent_id=? ORDER BY page_order ASC;");
$stmt->bind_param('s', $data->id);
$stmt->execute();

$stmt->store_result(); // Fetches results into a memory buffer
$num_of_rows = $stmt->num_rows;

$stmt->bind_result($child_id, $child_title, $child_visible, $child_parent);

while ($stmt->fetch()) {
  //...
}

echo($num_of_rows);

Remember to check the documentation for mysqli_num_rows() as such details are usually mentioned in the description section.

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