PHP MySQL multiple id insert and set name - php

Question

I've got this POST form in my website designed to make groups out of an unspecified number users. It works by while looping out all the users in my database with a check box next to their names. You tick the boxes of the users you want, give the group a name then submit the form.
To accomplish the above I need to do two queries due to the way the database has been set up. The table is called Participant/Group and it contains 3 columns: idParticipant, idGroup and GroupName. Here's what I have so far but it has its flaws:
$aParticipants = array_map('mysql_real_escape_string', $_POST['check']);
$pIn = implode("),(", $aParticipants);
$gIn = implode("', '", $aParticipants);
$query1 = mysql_query("INSERT INTO `Participant/Group` (`idParticipant`) VALUES ($pIn);");
$query2 = mysql_query("UPDATE `Participant/Group` SET GroupName = '".$_POST['group']."' WHERE idParticipant IN ('$gIn')");
So the first query inserts the id's of the users into the database and the second query adds the group name to each of those newly inserted id's. If you could combine these two queries I think it could solve all my problems but I'm pretty sure the syntax doesn't allow it.
Anyway the problem with the above code is that it overwrites the database with any subsequent overlapping queries. The important thing to remember here is users are not restricted to one group. A user with an id of 7 can be in a Group called Group A and also be in a group called Group C. There will need to be two separate rows to record this. With my code above it is creating the separate rows but both of them will have the group name of whatever was last submitted in the form.
Anyone know how my code could be tweaked (re-written if you want) to fix this?

Answer 1

Add group name in implode
$aParticipants = array_map('mysql_real_escape_string', $_POST['check']);
$group = mysql_real_escape_string($_POST['group']);
$pIn = implode(", {$group}),(", $aParticipants);
$query1 = mysql_query("INSERT INTO `Participant/Group` (`idParticipant`, `GroupName`) VALUES ($pIn);");

Answer 2

It could be done using only one query. Also, the group field must also be sanitized using mysql_real_escape_string to avoid SQL injection attacks.
$aParticipants = array_map('mysql_real_escape_string', $_POST['check']);
$group = mysql_real_escape_string($_POST['group']);
$sqlvalues = array();
foreach ($aParticipants as $p) {
$sqlvalues[] = "('$p', '$group')";
}
$values = implode(',', $sqlvalues);
mysql_query("INSERT INTO `Participant/Group` (`idParticipant`, GroupName)
VALUES $values");
For the sake of completeness, the best would be to use MySQLi or PDO to take advantage of prepared statements for the sake of performance and security.

Answer 3

$aParticipants = array_map('mysql_real_escape_string', $_POST['check']);
$participants = array();
foreach(aParticipants as $p) {
$participants[] = $p . ', ' . mysql_real_escape_string($_POST['group']);
}
$pIn = implode("),(", $participants);
$query1 = mysql_query("INSERT INTO `Participant/Group` (`idParticipant`, `GroupName`) VALUES ({$pIn})");
EDIT the problem here is that the $iPn string will contain ,( at the end that causes SQL error (which it did not when inserting just one value into one column).
Therefore a line
$pIn = implode("),(", $participants);
has to be replaced by
$pIn = substr(implode("),(", $participants), 0, -3);
Now it should work without any SQL errors...