此代碼是否循環遍歷MySQL返回的多行？

Question

我有下面的PHP代碼。它應該從數據庫中選擇多達10行，並將這些信息輸入到上面定義的數組中，以便稍後在代碼中打印並打印在頁面上。有三行應該選擇，但它只是選擇最新的一行。任何想法爲什麼？

//create arrays for storing each tests information 
$subject = array(); 
$tag = array(); 
$title = array(); 
$creator = array(); 
$creation_date = array(); 
$test_type = array(); 
$test_id = array(); 

$q = "SELECT test_id, title, subject, type, creation_date FROM tests WHERE user_id='$user_id' LIMIT 10"; //select first ten of users tests 
$r = mysqli_query ($dbc, $q) or trigger_error("Query: $q\n<br />MySQL Error: " . mysqli_error($dbc)); 

if (mysqli_affected_rows($dbc) > 0) //if the query ran correctly and the test details were gathered from the database 
{ 
    $i = 0; 

    while($row = mysqli_fetch_array($r, MYSQLI_ASSOC)) 
    { 
     $test_id[] = $row['test_id']; 
     $test_type[] = $row['type']; 
     $creation_date[] = $row['creation_date']; 
     $creator[] = $user_id; 
     $title[] = $row['title']; 
     $subject[] = $row['subject']; 

     $q = "SELECT tag_id FROM test_tags WHERE test_id='$test_id[$i]'"; //selects tags for test 
     $r = mysqli_query ($dbc, $q) or trigger_error("Query: $q\n<br />MySQL Error: " . mysqli_error($dbc)); 

     if (mysqli_affected_rows($dbc) > 0) //if the query ran correctly and the tag_ids were gathered from the database 
     { 
      while($row = mysqli_fetch_array($r, MYSQLI_ASSOC)) 
      { 
       $thisTag = $row['tag_id']; 

       $q = "SELECT name FROM tags WHERE tag_id='$thisTag' LIMIT 1"; //selects tag name 
       $r = mysqli_query ($dbc, $q) or trigger_error("Query: $q\n<br />MySQL Error: " . mysqli_error($dbc)); 

       if (mysqli_affected_rows($dbc) > 0)//if the query ran correctly and the tags were gathered from the database 
       { 
        while($row = mysqli_fetch_array($r, MYSQLI_ASSOC)) 
        { 
         $tag[$i][] = $row['name']; 
        } 
       } 
      } 
     } 
     $i++; 
    } 
}//end of SELECT if 

Answer 1

它看起來像你做的是一個多對多的數據庫。 （這意味着你有很多帖子連接到很多標籤）。
有兩件事，你在整個嵌套查詢中使用相同的行變量，並且你正在使用相同的結果變量。都應該避免。嘗試下面的代碼，並告訴我它是如何工作的。

<?php 
//create arrays for storing each tests information 
$subject = array(); 
$tag = array(); 
$title = array(); 
$creator = array(); 
$creation_date = array(); 
$test_type = array(); 
$test_id = array(); 

$q = "SELECT test_id, title, subject, type, creation_date FROM tests WHERE user_id='$user_id' LIMIT 10"; //select first ten of users tests 
$r1 = mysqli_query ($dbc, $q) or trigger_error("Query: $q\n<br />MySQL Error: " . mysqli_error($dbc)); 

if (mysqli_affected_rows($dbc) > 0) //if the query ran correctly and the test details were gathered from the database 
{ 
    $i = 0; 

    while($orow = mysqli_fetch_array($r1, MYSQLI_ASSOC)) 
    { 
     $test_id[] = $orow['test_id']; 
     $test_type[] = $orow['type']; 
     $creation_date[] = $orow['creation_date']; 
     $creator[] = $user_id; 
     $title[] = $orow['title']; 
     $subject[] = $orow['subject']; 

     $q = "SELECT tag_id FROM test_tags WHERE test_id='{$test_id[$i]}'"; //selects tags for test 
     $r2 = mysqli_query ($dbc, $q) or trigger_error("Query: $q\n<br />MySQL Error: " . mysqli_error($dbc)); 

     if (mysqli_affected_rows($dbc) > 0) //if the query ran correctly and the tag_ids were gathered from the database 
     { 
      while($irow = mysqli_fetch_array($r2, MYSQLI_ASSOC)) 
      { 
       $thisTag = $irow['tag_id']; 

       $q = "SELECT name FROM tags WHERE tag_id='{$thisTag}' LIMIT 1"; //selects tag name 
       $r3 = mysqli_query ($dbc, $q) or trigger_error("Query: $q\n<br />MySQL Error: " . mysqli_error($dbc)); 

       if (mysqli_affected_rows($dbc) > 0)//if the query ran correctly and the tags were gathered from the database 
       { 
        while($iirow = mysqli_fetch_array($r3, MYSQLI_ASSOC)) 
        { 
         $tag[$i][] = $iirow['name']; 
        } 
       } 
      } 
     } 
     $i++; 
    } 
}//end of SELECT if 
?>