PhP，MySql - 优化代码

Question

我不是一个伟大的PHP编码器（我来自C++）。我只使用PHP进行数据库输入。

我有以下数据库：

UserId (an unique int) 
AsyncPointsAverage (float) 
AsyncPointsAverageRank (a position based on the value immediately above) 
AsyncPointsRecentAverage (float an average for the last 5 tests only) 
AsyncPointsRecentAverageRank (a position based on the value immediately above) 

有在该表中大约1000-1500项。每天早上和下午5人进行测试，影响他们的整体平均水平和最近的平均水平。 （这是其他地方更新的内容，但这里没有显示。）之后，对这5个人进行计算，然后所有1000-1500的排名都会生效，所以我写下了下面的代码。它是最佳的吗？

我最关心的是我正在做1000次的MySql UPDATE。这很棒吗？我应该以另一种方式去做吗？ （也觉得免费优化功能的任何其他代码。正如我说的，我是从C++背景，所以真的不知道PHP的细微差别。）

// Sorts by array entry 1 
function ReRankCompareAverage($a, $b) 
{ 
    if($a[1] == $b[1]) return 0; 
    else return ($a[1] > $b[1] ? 1 : -1); 
} 
// Sorts by array entry 2 
function ReRankCompareAverageRecent($a, $b) 
{ 
    if($a[2] == $b[2]) return 0; 
    else return ($a[2] > $b[2] ? 1 : -1); 
} 

function ReRank($db) 
{ 
    $i = 0, $j = 0; 
    $usersARR = null; 

    $stmt = $db->prepare("SELECT UserId, AsyncPointsAverage, AsyncPointsRecentAverage FROM studenttable"); 
    $stmt->execute(); 
    if($stmt && isset($stmt) && $stmt->rowCount() > 0) 
    { 
     $i = 0; 
     while(($row = $stmt->fetch(PDO::FETCH_ASSOC))) 
     { 
      $usersARR[$i][0] = intval($row['UserId']); 
      $usersARR[$i][1] = floatval($row['AsyncPointsAverage']); 
      $usersARR[$i][2] = floatval($row['AsyncPointsRecentAverage']); 
      $i++; 
     } 
    } 
    $stmt->closeCursor(); // mysql_free_result equivalent 

    // The first pass of $j == 3 does the ranking by Average, filling position $usersARR[][3] with that rank 
    // The second pass of $j == 4 does the ranking by AverageRecent, filling position $usersARR[][4] with that rank 
    for($j = 3, $j <= 4; $j++) 
    { 
     $iCompare = $j == 3 ? 1 : 2; 

     usort($usersARR, $j == 3 ? "ReRankCompareAverage" : "ReRankCompareAverageLast"); 
     $count = count($usersARR); 
     if($count > 0) 
     { 
      // Start it off, with the person with the highest average is rank 1 
      $usersARR[$count - 1][$j] = 1; // Position $j is filled with the rank 
      // Now loop starting from the second one down 
      for($i = $count - 2, $rank = 1; $i >= 0; $i--) 
      { 
       // Only change the rank if the next one down is strictly lower than the one above, otherwise will share the same rank 
       if($usersARR[$i][$iCompare] < $usersARR[$i+1][$iCompare]) $rank = $count - $i; // Otherwise keep the same rank, because they are equal 
       $usersARR[$count - 1][$j] = $rank; 
      } 
     } 
    } 

    // Now $usersARR is filled with the correct rankings, and they are asscoiated with $UserId 
    // Now we must put all of these rankings into the database 
    $count = count($usersARR); 
    for($i = 0; $i < $count; $i++) 
    { 
     $stmt = $db->prepare("UPDATE studenttable SET AsyncPointsAverageRank=:AsyncPointsAverageRank, AsyncPointsRecentAverageRank=:AsyncPointsRecentAverageRank " 
         . "WHERE UserId=:UserId"); 
     $stmt->execute(array(':AsyncPointsAverageRank' => $usersARR[$i][3], 
         ':AsyncPointsRecentAverageRank' => $usersARR[$i][4], 
         ':UserId' => $usersARR[$i][0])); 
    } 
} 

Answer 1

需要如何使用排名？也许你存储Ranks是不必要的？他们可能很容易计算：

SELECT COUNT(*) 
FROM studenttable 
WHERE AsyncPointsAverage > $currentUserVariableAsyncPoints 

要显示TOP 10：

SELECT * FROM studenttable ORDER BY AsyncPointsAverage DESC LIMIT 0,10 

等

编辑：

，以显示与位置编号完整的排名，你可以做到这一点在PHP（你已经有了 - 在循环内部，你可以获取行，只显示$i++变量）。或者你可以用纯SQL尝试（我个人比较喜欢）：

SET @rank=0; SELECT @rank := @rank +1 AS rank, UserId, AsyncPointsAverage 
FROM studenttable 
ORDER BY AsyncPointsAverage DESC 

Answer 2

只是对马克的回答展开，你不需要每次添加一个测试结果的时间重新计算排名。这当然是功能性的，但它不是最佳的。最好的方法是在显示它时计算排名。如果您希望允许学生获得相同的结果和相同的排名，则可以始终使用PHP计算排名。

SQL：

SELECT 
    UserId, 
    AsyncPointsAverage, 
    AsyncPointsAverageRank 
FROM 
    studenttable 
ORDER BY 
    AsyncPointsAverage DESC 

PHP：

$stmt = $db->prepare("SEE ABOVE..."); 
$stmt->execute(); 

if($stmt && isset($stmt) && $stmt->rowCount()) { 
    $rank = 1; 
    $last_grade = -1; 

    while(($row = $stmt->fetch(PDO::FETCH_ASSOC))) { 
     $usersARR[$i][0] = intval($row['UserId']); 
     $usersARR[$i][1] = floatval($row['AsyncPointsAverage']); 
     $usersARR[$i][2] = floatval($row['AsyncPointsRecentAverage']); 

     if($usersARR[$i][1] < $last_grade) { 
      $rank++; 
     } 

     $usersARR[$i][3] = $rank; 

     $last_grade = $usersARR[$i][1]; 
    } 
} 

你只需要改变字段读取和ORDER BY领域，如果你想通过最近的平均订购吧。