need to test if sql query was successful

I have this query and if it returns successful, I want another function to process, if not, do not process that function.

Here is the code for running the query

global $DB;
$DB->query("UPDATE exp_members SET group_id = '$group_id' WHERE member_id = '$member_id'");

I imagine it is something like…

if($DB) { 
    //success 
} else { 
    //failure 
}

Answer

This is the simplest way you could test

$query = $DB->query("UPDATE exp_members SET group_id = '$group_id' WHERE member_id = '$member_id'");

if($query) // will return true if succefull else it will return false
{
// code here
}