PHP为什么这段代码不回应？

After executing the following code, $i doesn't echo if I have the $q3 delete query enabled. If I comment it or delete $q3, then everything is fine.

How can I get this to work?

$isfound = in_array("empty",$currentrooms0);
if($isfound===true){
    for($i=0; $i<count($currentrooms0);$i++){
        if($currentrooms0[$i]=="empty"){
            $q3=mysqli_query($conn0,"delete from room_attributes where _current_created_rooms='empty' order by id desc limit 1")or die(mysqli_error($conn0));    
            echo $i-1;
            break;
        }
    }

The reason it won't echo is because there is an error in your SQL and mysqli_query returns false in such case.

The SQL causes an error because you cannot use ORDER BY inside a WHERE clause that directly belongs to a DELETE

If what you are looking to delete the topmost attribute then you might want to consider using this sql and your code should work.

DELETE FROM room_attributes
WHERE id IN (
  SELECT id FROM room_attributes
  WHERE _current_created_rooms='empty'
  ORDER BY id DESC
  LIMIT 1
)

I think you have problem with mysqli_connect please try to do following ..

if($q3 ===TRUE){
    echo $i-1;
    break;
}else{
    echo "Connection Problem";
}

The OP wrote:

here is the answer:

$isfound = in_array("empty",$currentrooms0); 
if($isfound===true){ 
    for($i=0; $i<count($currentrooms0);$i++){ 
        if($currentrooms0[$i]=="empty"){ 
            $q3=mysqli_query($conn0,"delete from room_attributes where _current_created_rooms='empty' order by id desc limit 1") or die(mysqli_error($conn0)); 
            if(i>$i-1) {echo 0;}else{echo $i-1;} 
            break; 
         } 
    }