MySQL Update Fix Two rows with one query - php

Question

This is the code giving me issue - I'm trying to update multiple records with one insert. The values are put in an array and using a foreach I've prepared the mysqli update. But it's not working. Just gives a MySqli error about the syntax on the update.
foreach($users as $user){
if(empty($course)) continue;
$query_string .= " SET group_id='$group_id' WHERE user_id='".$user."'; ";
}
$query_string = substr($query_string,0,-1);
$query = "UPDATE users" . $query_string;
$result = mysqli_query($dbc, $query) or trigger_error("Query: $query");
The error it gives is:
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SET group_id='10' WHERE user_id='5''. I think it's the ';' in the middle that mysqli isn't accepting.

Answer 1

Assuming you've got more than one user, your query will look like
UPDATE users SET ... SET ... SET ... SET ...
which is incorrect. You cannot do updates to multiple rows in this fashion. Either do multiple queries, each updating one student, or you'll have to build a huge case/if block to do this in a single query.
You'd be better off doing the multiple queries, as you'll probably spend more time BUILDING the monolithic query than it'd take to run the individual updates.

Answer 2

How about WHERE...IN
UPDATE foo SET bar = 0 WHERE baz IN (1,2,3,4,5,6)
(presuming that you are setting them all to the same group ID, which is not clear in the context provided)

Answer 3

try this code:
<?php
$queries = array();
foreach($users as $user){
if(empty($course)) continue;
$queries[] = "update users set group_id = '" . mysql_real_escape_string($group_id) . "' where user_id = '" . mysql_real_escape_string($user) . "'";
}
array_map('mysql_query', $queries);
?>

Answer 4

Your problem is that you don't separate the different users with ;. Since you're updating all users to have the same group (I'm not sure this is the case, otherwise it will get much more complex) you can simply expand the criteria with OR. Your resulting query would look something like the following:
UPDATE users SET group_id='42' WHERE user_id='1' OR user_id='2' OR user_id='3';
Another solution would be to use WHERE ... IN. Here's an example of that:
UPDATE users SET group_id='42' WHERE user_id IN (1, 2, 3);