PHP prepared statement error on UPDATE

Question

I have this PHP Prepared statements code:

/* Register a prepared statement */
        if ($stmt = $mysqli->prepare('UPDATE house_room1 SET rotation = (rotation + 1) % 4 WHERE ref_id = ?')) {

                /* Bind parametres */
                $stmt->bind_param('i', $item_number);

                /* Execute the query */
                $stmt->execute();

                /* Bind results */
                $stmt->bind_result($rotation);

                /* Fetch it */
                $stmt->fetch();

                /* Close statement */
                $stmt->close();

            } else {
                /* Something went wrong */
                echo 'Something went terribly wrong'     . $mysqli->error;
            }

The problem is that I get an error saying: mysqli_stmt::bind_result(): Number of bind variables doesn't match number of fields in prepared statement in /blablabla/bla/database/update_settings_rotate.php on line 21

Line 21 is where I bind results.

Okay, so I guess it has something to do with the fact that rotation is equal to something and not appeared as a "?" which it usually shall be in prepared statements. I tried changing that but how there was still errors. hm I don't think it will know what rotation is equal to when its changed to a variable, or else it wont let me bind the parameter as an integer since I am dividing. Even though it will always be a real number. Any ideas? hm

I guess there are some problems binding results when it's an update statement, but I don't know how I would get that out in any way? Are there any better ways?

Answer 1

在更新查询中使用方括号

if ($stmt = $mysqli->prepare('UPDATE house_room1 SET rotation = ((rotation + 1) % 4) WHERE ref_id = ?')) {

Answer 2

Try this

/* Register a prepared statement */
        if ($stmt = $mysqli->prepare('UPDATE house_room1 SET rotation = (rotation + 1) % 4 WHERE ref_id = :val')) {

            /* Bind parametres */
            $stmt->bind_param(':val', $item_number);

            /* Execute the query */
            $stmt->execute();

            /* Bind results */
            $stmt->bind_result($rotation);

            /* Fetch it */
            $stmt->fetch();

            /* Close statement */
            $stmt->close();

        } else {
            /* Something went wrong */
            echo 'Something went terribly wrong'     . $mysqli->error;
        }

Answer 3

Not much incorrect with your original code. I haven't changed your update query. The issue you had was trying to read the updated value from the 'update' statement.

Not pretty code, i have left some debugging code in. I was rather pedantic with the syntax. All the backticks are redundant. I do not use all the variables such as 'allOk'. I did use them earlier while i was debugging / checking the code.

It is tested and works on PHP 5.3.18, mysql 5.5.16 on windows XP.

It updates the database and then shows the updated value.

<?php
/* Q22377771 :

/* */

// new connection
$db = new mysqli('localhost', 'test', 'test', 'testmysql');


// ref_id of row to update...
$item_number = 1;

// the update statement
$stmt = $db->prepare('UPDATE `house_room1` SET `rotation` = (`rotation` + 1) % 4 WHERE `ref_id` = ?');

echo '<br/>prepare error: ', $db->errno, ' : ', $db->error, '<br/>';

/* Bind parametres */
$stmt->bind_param('i', $item_number);

// execute the update..
if ($allOk = $stmt->execute()) {
    if ($db->affected_rows >= 1) {
      echo '<br/>record updated!<br/>';
    }
    else {
      echo '<br/>record NOT updated!<br/>';
    }
}
else{
    var_dump($db->affected_rows, $stmt->affected_rows, $allOk. $db->sqlstate, $stmt->sqlstate);
    echo 'update error', $db->errno, ' : ', $db->error, '<br/>';
}

/* Close statement */
$stmt->close();
unset($stmt);

/* -------------------------------------------------------
 * Now read the row so that we can get the rotation value
 */

// result in here...
$rotation = -1;

// the query statement
$stmt = $db->prepare('select  `rotation` FROM `house_room1` WHERE `ref_id` = ?');

echo '<br/>prepare error: ', $db->errno, ' : ', $db->error, '<br/>';

/* Bind parametres */
$stmt->bind_param('i', $item_number);

$allOk = $stmt->execute();

/* Bind results */
$stmt->bind_result($rotation);

/* Fetch it */
$stmt->fetch();

// show result...
var_dump('rotation : '. $rotation);

/* Close statement */
$stmt->close();

$db->close();
?>