如何用PHP增加MySQL數據庫中的某些行？

Question

我有這個PHP：

$adj_index = $currentSignup + 1 - $r;//$r=3 and $currentSignup=24 
for($i=1; $i<$referrals; $i++){ 
    $current_index = $currentSignup + 1 - $i; 
    $q = "SELECT signup_id FROM app_sign_ups WHERE (adjusted_index='$current_index' AND app_id='$app_id')"; 
    $r = mysqli_query ($dbc, $q) or trigger_error("Query: $q\n<br />MySQL Error: " . mysqli_error($dbc)); 

    $next_index = $current_index + 1; 
    if (mysqli_num_rows($r) == 1){ 
     $row = mysqli_fetch_array($r, MYSQLI_ASSOC); 
     $signuper = $row['signup_id']; 
     $q = "UPDATE app_sign_ups SET adjusted_index='$next_index' WHERE (app_id='$app_id' AND signup_id='$signuper')"; 
     $r = mysqli_query ($dbc, $q) or trigger_error("Query: $q\n<br />MySQL Error: " . mysqli_error($dbc)); 
    } 

} 

$q = "UPDATE app_sign_ups SET adjusted_index='$adj_index' WHERE app_s_id='$app_s_id'"; 
$r = mysqli_query ($dbc, $q) or trigger_error("Query: $q\n<br />MySQL Error: " . mysqli_error($dbc)); 

它應該在我的數據庫更新的行。每行有一個從1到25的值（adjusted_index）。有了它，我拿到了25號，22號（通過從原來的號碼[25]中刪除$r），並將前一個22-24各移動一個（到23,24,25）。由於某種原因，當我運行它導致22,24,25,22而不是23,24,25,22就像我想要的那樣。我已經做了一些其他組合，看起來有adjusted_index被最後一行替換（22被25替換）。

Answer 1

只運行一個UPDATE聲明，一旦：

$q = " UPDATE app_sign_ups 
     SET adjusted_index = adjusted_index 
          + CASE WHEN adjusted_index < 25 
           THEN 1 
           ELSE - '$r' 
          END 
     WHERE adjusted_index >= 25 - '$r' 
     AND app_id = '$app_id' 
     ORDER BY adjusted_index 
    "; 

---

，或者甚至更好，有2點UPDATE聲明：

$q1 = " UPDATE app_sign_ups 
     SET adjusted_index = adjusted_index + 1 
     WHERE adjusted_index >= 25 - '$r' 
      AND app_id = '$app_id' 
     ORDER BY adjusted_index DESC    --- this line is needed if 
    ";           --- you have a UNIQUE index on 
                --- (app_id, adjusted_index) 

$q2 = " UPDATE app_sign_ups 
     SET adjusted_index = 25 - '$r' 
     WHERE adjusted_index = 26 
      AND app_id = '$app_id' 
    ";