查询无法保存

Question

I made this query to show me the 'rank' of the Result ordered by there points. The query works fine but for some reason, I did not get any results whent trying to fetch it with php Maybe someone can tell me why?

(int) $a    = $_GET['a'];
if($ranking = $con->prepare("SET @rownum := 0; SELECT rank, id FROM (SELECT @rownum := @rownum + 1 AS rank, id FROM anime ORDER BY points DESC) as result WHERE id=$a"))
{
    $ranking->execute();
    $ranking->next_result();
    $ranking->bind_result($rank, $id);

    while($ranking->fetch()) 
    {
        var_dump($rank, $id);
        if($id == $a)
        {
          echo "<span class='rnknr'>#$rank</span>";
        }
    }

    $ranking->close();
}

}

Answer 1

$ranking->execute(); may return multiple resultsets if query contains more than 1 expression.

Answer 2

Try this

(int) $a    = $_GET['a'];
if($ranking = $con->prepare("SET @rownum := 0; SELECT rank, id FROM (SELECT @rownum := @rownum + 1 AS rank, id FROM anime ORDER BY points DESC) as result WHERE id=1"))
{
    $ranking->execute();
    $ranking->next_result(); //<- advance to the result set for 2nd query (The select query)
    $ranking->bind_result($rank, $id);

    while($ranking->fetch()) 
    {
    if($id == $a)
        {
          echo "<span class='rnknr'>#$rank</span>";
        }
    }

    $ranking->close();
}

You have 2 queries in your statement so only calling fetch will give you the result of the first query SET @rownum := 0 . You need to advance to the 2nd result set by calling next_result

Answer 3

You must use some special method from mysqli::multi_query because this is multi query :) Now your code could look like this:

$mysqli = mysqli_connect(HOST, USER, PASS, DB);

#(int) $a = $_GET['a']; -> What is this ?

$a = (int)$_GET['a']; //This is simplest casting

$sql = 'SET @rownum := 0; SELECT rank, id FROM (SELECT @rownum := @rownum + 1 AS rank, id FROM anime ORDER BY points DESC) as result WHERE id='.$a;
if ($mysqli->multi_query($sql)) {
    $mysqli->next_result();
    $result = $mysqli->store_result();
    while ($row = $result->fetch_assoc()) {
        if($row['id'] == $a)
        {
          echo "rank: #{$row['rank']}";
        }
    }
}