Joel Joel - 7 months ago 10
SQL Question

MySQLi multiple prepare statements

I have checked everywhere thoroughly, and have gone through everything possible to find an answer to this. Besides saying "the code doesn't work" which obviously is not enough, I have yet to find anything that will even come close to this. I'm probably going to get downvotes, but let's see how this goes.

I am learning how to do prepared statements for a search query from the user end, and I have to do it for multiple queries. I have to bind parameters to these multiple queries, and then execute them and use them and receive multiple rows. This is most of my code, and what I currently have is not reporting any errors whatsoever. It just returns a blank white page.

I am doing this from a simple test.php file, and those are the results I'm getting.

Now for the code.

$prep1 = $test->prepare("SELECT * FROM sb__bans WHERE sb__bans.authid=? ORDER BY sb__bans.bid DESC");
$prep2 = $test->prepare("SELECT * FROM sb__bans AS bans INNER JOIN sb__admins AS admins ON bans.aid = admins.aid WHERE bans.authid=? ORDER BY bans.bid DESC");
$prep3 = $test->prepare("SELECT * FROM sb__bans AS bans INNER JOIN sb__servers AS servers ON bans.sid = servers.sid WHERE bans.authid=? ORDER BY bans.bid DESC");

$search = "steam";

$prep1->bind_param("s", $search);
$prep2->bind_param("s", $search);
$prep3->bind_param("s", $search);

$prep1->execute();
$prep2->execute();
$prep3->execute();

while($row = $prep1->fetch() && $admin = $prep2->fetch() && $sv = $prep3->fetch()) {
echo $row['test'];
echo $admin['test'];
echo $sv['test'];
}


The database is initialized above this as
$test = new mysqli("localhost", "test", "test", "test");


$search = "steam"
steam would be replaced with the the post variable of course, but for testing reasons I've removed that for now and am testing with just a simple variable.

What seems to be the problem here?

Thanks in advance.

Answer

Two points:

  1. Based on personal experience, you can only have one prepared statement in existence at a time. I suspect this is because the db requires each PS to have a session-unique name, and the PHP layer is passing some common default name rather than generating a unique name for each PS. By comparison, the PostgreSQL driver allows an optional name for each PS, but still allows only one unnamed PS to exist. Essentially this means that you must prepare, bind, execute and fetch one PS completely before you can prepare the next PS.

  2. You're misusing mysqli_stmt::fetch(). fetch() returns only true or false, and is used to update variables which have previously been bound with mysqli_stmt::bind_result(). To retrieve values into a $row array, you must first call mysqli_stmt::get_result() to return a mysqli_result, and then call mysqli_result::fetch_array().

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