Whats wrong with the syntax in my mysql select statement (php, mysql) - php

Question

I have a table and i'm trying to extract the maximum value of a column called order_num, which has 33 intries of integers 1 through 33. I want the value "33" in this instance as its the highest number.
$userid is an integer derived from a one row table with a field id that I am trying to retrieve
//get the currentUser ID so we know whos deck to ammend
$userIDSQL = "SELECT id FROM currentUser";
$userIdResult = mysqli_query($db, $userIDSQL) or die("SQL Error on fetching user ID: " . mysqli_error($db));
$result_array = array();
while ($row = mysqli_fetch_assoc($userIdResult)) {
$result_array[] = $row['id'];
}
//the actual user id
$userId = $row['id'];
echo "user id is " . $userId;
Doing a print_r on $userId shows the array to be empty, that's why the code below doesn't work.. :(
...
$reOrderDeckSQL = "SELECT MAX(order_num) AS order_num FROM decks WHERE id='$userId'";
$reOrderDeckResult = mysqli_query($db, $reOrderDeckSQL) or die("SQL Error on reOrder: " . mysqli_error($db));
$result_array = array();
while ($row = mysqli_fetch_array($reOrderDeckResult)) {
$result_array[] = $row['MAX(order_num)'];
echo "the result is" . $result_array['order_num'];
echo "the result is" . $row['order_num'];
echo "the result is" . $result_array['MAX(order_num)']; //tried different methods to get the output.
}
The output I get is
the result is the result is the result is
Does anyone know why i'm not able to get the result from the table?

Answer 1

Edit:
Okay, try this:
while ($row = mysqli_fetch_array($reOrderDeckResult)) {
print_r($row);
}
What do you get?

Answer 2

Your first code to get the userId doesn't work because of your usage of the array, change to:
$userId = 0;
while ($row = mysqli_fetch_assoc($userIdResult)) {
$userId = $row['id'];
}
As I've shown below, if you only expect a single row then remove the while loop and just call fetch_assoc a single time.
Given you only want the single row you don't need the while loop:
$reOrderDeckSQL = "SELECT MAX(order_num) AS order_num FROM decks WHERE id='$userId' LIMIT 1";
$reOrderDeckResult = mysqli_query($db, $reOrderDeckSQL) or die("SQL Error on reOrder: " . mysqli_error($db));
if($reOrderDeckResult && mysqli_num_rows($reOrderDeckResult) == 1)
{
$row = mysqli_fetch_assoc($reOrderDeckResult);
echo 'result: ' . $row['order_num'];
}
else
{
echo 'No rows found!!';
}
I also added LIMIT 1 to the query, and a check to see if there are any rows.

Answer 3

You have renamed your MAX(order_num) AS order_num so you should try to get value using order_num only as echo $result_array['order_num']
and in while you should check whether you are getting value or not by placing below code in while loop
echo '<PRE>';
print_r($row);
echo '</PRE>';

Answer 4

This may helps you..,
<?php
$reOrderDeckSQL = "SELECT MAX(order_num) AS order_num FROM decks WHERE id='$userId'";
$reOrderDeckResult = mysqli_query($db, $reOrderDeckSQL) or die("SQL Error on reOrder: " . mysqli_error($db));
$result_array = array();
while ($row = mysqli_fetch_array($reOrderDeckResult)) {
//you have to use the alias name not aggregate function title
$result_array[] = $row['order_num'];
echo "the result is" . $result_array['order_num'];
echo "the result is" . $row['order_num'];
//you have to use the alias name not aggregate function title
echo "the result is" . $result_array['order_num']; //tried different methods to get the output.
}