num_rows doesn't work with prepared statement [closed] - php

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I have a test code where I try to reach my database information. But one script that uses prepared statements does not work, and second without prepared statements works just fine.
$userzzz = "test";
With this script, I get "BAD" as the result
$db = new mysqli("localhost", "root", "", "test");
$stmt = $db->prepare('SELECT * FROM user WHERE username=?');
$stmt->bind_param('s', $userzzz);
$stmt->execute();
echo $stmt->num_rows();
if ($stmt->num_rows > 0){
echo "good";
} else {
echo "bad";
}

Answer 1

From the manual,
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.
Which means that you'll have to use $stmt->store_result(); after executing, but before accessing the num_rows property.
$stmt = $db->prepare('SELECT * FROM user WHERE username=?');
$stmt->bind_param('s', $userzzz);
$stmt->execute();
$stmt->store_result();
echo $stmt->num_rows;
if ($stmt->num_rows > 0){
echo "good";
} else {
echo "bad";
}
If you don't do this, the rows won't be buffered into the memory, and there's no way of knowing how many rows actually was returned, until you loop through the entire set of data (by while ($stmt->fetch())).
PHP.net on mysqli_stmt_store_result()

Answer 2

in object oriented mysqli, num_rows is not a function, it's an attribute of the result (stmt). You need $stmt->num_rows; not $stmt->num_rows();
In your second example, you're not using (), you are doing it correctly, hence why it functions in the second but not the first.
$db = new mysqli("localhost", "root", "", "test");
$stmt = $db->prepare('SELECT unique_col FROM user WHERE username=?');
$stmt->bind_param('s', $userzzz);
$stmt->execute();
$stmt->store_result();
$rows = $stmt->num_rows;
if ($rows > 0){
echo "good";
} else {
echo "bad";
}
I also added $stmt->store_result(). It is finicky and num_rows will be 0 unless you store the result before you run $stmt->num_rows;
I'd also use a unique column instead of *, such as id for example.

Answer 3

Well you need to bind the results after you execute, this will work in your case (works for me):
<?php
$userzzz = 'test';
$db = new mysqli("localhost", "root", "", "test");
$stmt = $db->prepare('SELECT * FROM users WHERE username = ?');
$stmt->bind_param('s', $userzzz);
$stmt->execute();
$stmt->store_result();
echo $stmt->num_rows();
if ($stmt->num_rows() > 0){
echo "good";
} else {
echo "bad";
}
?>