ORDER BY 在 PHP/MySQL 中没有按预期工作

Question

My code:

$afer_result = mysql_query("SELECT * FROM aq_afers WHERE aferId = '".$afer_id."'");

while ($afer = mysql_fetch_array($afer_result)) {
$item_result = mysql_query("SELECT * FROM aq_".$afer['ItemCategory']."s WHERE ItemId = '".$afer['ItemId']."' ORDER BY ItemLevel");
$item = mysql_fetch_assoc($item_result);

echo $item['ItemLevel'];
echo "\n";
}

I expect the output to be a list of numbers to be sorted from lowest to highest, but this is what my output looks like:

10
37
62
15
35
55
75
95
105
70
40
50
15
35
1
55

Any idea why ORDER BY is not working as I expect it to?

Answer 1

The problem with your code is that you run several queries within a loop. The results of each query are ordered, but not the global results.

A solution is to use the loop to build a UNION sql query. The you can run the query outside the loop ; the ORDER BY clause of an UNION query applies globally to its results. Of course this assumes that all queries return the same columns (else you'll need to adapt the code).

Code ;

$afer_result = mysql_query(
    "SELECT * 
    FROM aq_afers 
    WHERE aferId = '".$afer_id."'"
);

$sql_parts = array();
while ($afer = mysql_fetch_array($afer_result)) {
    array_push(
        $sql_parts,
        "SELECT * 
          FROM aq_".$afer['ItemCategory']."s
          WHERE ItemId = '".$afer['ItemId']."'"
    );
}

$sql = join(' UNION ALL ', $sql_parts);
$item_result = mysql_query($sql . 'ORDER BY ItemLevel');
while ($item = mysql_fetch_array($item_result)) {
    echo $item['ItemLevel'];
    echo "\n";
}

Answer 2

Your code select the categories and goes throug each of them. It selects the ItemLevel for each category sorted, but not all of them at the same time. For the first category 10, 37, 62 For the second category: 15, 35, 55, 75, 95, 105 For the third category: 70 Etc.

So you should merge your 2 sql queries into one and order that result.
If it is not possible you should store the itemlevels into an array and sort it before printing them out.

$afer_result = mysql_query("SELECT * FROM aq_afers WHERE aferId = '".$afer_id."'");
$itemLevels = [];
while ($afer = mysql_fetch_array($afer_result)) {
    $item_result = mysql_query("SELECT * FROM aq_".$afer['ItemCategory']."s WHERE ItemId = '".$afer['ItemId']."' ORDER BY ItemLevel");
    $item = mysql_fetch_assoc($item_result);
    $itemLevels[] = $item['ItemLevel'];
}
asort($itemLevels);
foreach ($itemLevels as $itemLevel) {
    echo $itemLevel;
    echo "\n";
}