MySQL - 在不同的查询中执行选择和删除？

Question

I was wondering how would go about executing two different queries like this:

    if ($uresult->num_rows >0) {


 while($urow = $uresult->fetch_assoc()) {


 $rresult = mysqli_query($con,"SELECT * FROM allid WHERE postid='$oldid' AND spaceid='$newid'");
 $rresult = mysqli_query($con,"DELETE FROM allid WHERE postid AND spaceid IS NULL");
 $lrow = mysqli_fetch_assoc($rresult);
 $tem = $lrow['postid'];

 $ujson = json_encode($tem);
 echo $ujson;
 }

} else {
}

I know mysqli_fetch can't hold no more than one query and there are similar questions, but I can't seem to understand the answers from the other questions. If there is a question that solves this question, I apologize and will delete this one.

Answer 1

all other things being equal, simple dont overwrite the $rresult from select with delete:

if ($uresult->num_rows >0) {

    while($urow = $uresult->fetch_assoc()) {
        $rresult = mysqli_query($con,"SELECT * 
                                      FROM allid 
                                      WHERE postid='$oldid' 
                                      AND spaceid='$newid'");
        mysqli_query($con,"DELETE FROM allid 
                           WHERE postid AND spaceid IS NULL");
        $lrow = mysqli_fetch_assoc($rresult);
        $tem = $lrow['postid'];

        $ujson = json_encode($tem);
        echo $ujson;
    }

} else {
}