选择查询不适用于链接表（mysql）

$sql=mysql_query("SELECT b.book_id,u.user_id,user_name,book_name,review_date,book_rating,review 
        FROM tbl_books b,tbl_user u,tbl_book_reviews br 
        WHERE b.book_id=br.book_id 
        AND u.user_id=br.user_id 
        AND moderated='n' 
        ORDER BY review_date ASC 
        LIMIT 1");

我想知道上面的select查询的结构是否是错误的？因为它为tbl_books.book_id和tbl_user.user_id返回空白。但是，我得到了其他领域的正确值。选择查询不适用于链接表（mysql）

下面是缓和书评的完整代码：

<?php 
session_start(); 

if (!isset($_SESSION['user_id']) || !isset($_SESSION['user_name']) || !isset($_SESSION['password'])) { 
    echo "Your session has timed out."; 
    exit();} 
$errormsg=""; 
include "scripts/connect_to_mysql.php"; 
?> 
<html> 

<head> 

<link rel="stylesheet" type="text/css" href="reset.css" media="screen" /> 
<link rel="stylesheet" type="text/css" href="style1.css" media="screen" /> 
<title>Moderate Reviews</title> 

<body> 

<div id="layout_wrapper"> 
<div id="layout_container"> 
<div id="layout_content"> 

    <div id="site_title"> 
     <h1><a href="home.php"></a></h1> 
     <h2></h2> 
    </div> 

    <?php include "header.php";?> 

<?php include "navi_admin.php";?> 

     <div class="clearer">&nbsp;</div> 

    <div id="main"> 

     <div class="post"> 

      <div class="post_top"> 
       <div class="post_title"><h2>Moderate Reviews</h2></div> 
      </div> 

      <div class="post_body"> 



    <?php 
      if (isset($_POST['mod_save'])) 
    { 
    $b_id=mysql_real_escape_string($_POST['book']); 
    $u_id=mysql_real_escape_string($_POST['user']); 
     if ($_POST['mod_action']=="a"){ 
     $sql=mysql_query("UPDATE tbl_book_reviews SET moderated='a' WHERE moderated='n' WHERE book_id='$bid' AND user_id='$uid'"); 
     $errormsg="Your moderation action has been successfully saved. You may now moderate the next review below."; 
     } 
     else if($_POST['mod_action']=="r") 
     { 
      $sql=mysql_query("UPDATE tbl_book_reviews SET moderated='r' WHERE book_id='$bid' AND user_id='$uid' AND moderated='n'"); 
     $errormsg="Your moderation action has been successfully saved. You may now moderate the next review below."; 
     } 
     else 
     { 
     $errormsg="Please select a moderation action."; 
     } 
    } 
?> 
    <?php 
$sql=mysql_query("SELECT b.book_id,u.user_id,user_name,book_name,review_date,book_rating,review 
        FROM tbl_books b,tbl_user u,tbl_book_reviews br 
        WHERE b.book_id=br.book_id 
        AND u.user_id=br.user_id 
        AND moderated='n' 
        ORDER BY review_date ASC 
        LIMIT 1"); 
$Rs=mysql_num_rows($sql); 
if($Rs<1) 
    { 
     $errormsg="There is no new book reviews that need moderation."; 
    } 
else 
    { 
     while ($row=mysql_fetch_array($sql)) 
     { 
     $bid=$row['b.book_id']; 
     $bname=$row['book_name'];  
     $review_author=$row["user_name"]; 
     $uid=$row['u.user_id']; 
     $date=$row["review_date"]; 
     $whenReview= strftime("On %b %d, %Y",strtotime($date)); 
     $review_body=$row["review"]; 
     $rating=$row["book_rating"]; 
    } 
    } 

    ?> 
    <div><i>Breadcrumbs: </i><a href="admincontrol.php">Admin Home</a></div><br/> 
    <?php if ($errormsg=="There is no new book reviews that need moderation.") 
      {echo $errormsg; 
      echo '<br/><br/>';} 
      else 
      {?> 
    <table> 
    <tr><td><?php echo $whenReview;?>&nbsp; <?php echo $review_author;?> gave a rating of <?php echo $rating;?> on <?php echo $bname;?> and said:</td></tr> 
    <tr><td><?php echo $review_body;?></td></tr> 
    <tr><td><form action="" method="POST" name="mod_form"> 
    Choose your action: <select name="mod_action" id="mod_action"> 
    <option value="n" selected>Please select</option> 
    <option value="a">Accept</option> 
    <option value="r">Reject</option> 
    </select> 
    <input name="book" id="book" value="<?php echo $bid;?>"/> 
    <input type="hidden" name="user" id="user" value="<?php echo $uid;?>"/> 
    <input type="submit" name="mod_save" id="mod_save" value="Save Moderation"/> 
    </form> 
    </td></tr> 
    </table> 
    <?php }?> 
    </div> 

     <div class="clearer">&nbsp;</div> 


    <?php include "footer.php";?> 

</div> 
</div> 
</div> 
</div> 
</div> 
</body> 
</html> 

[/code]

来源

2011-04-24 yurimano

查询的结构是没有错的。这是错误的：

$bid=$row['b.book_id'];

，这是错误的：

$uid=$row['u.user_id'];

使用

$bid=$row['book_id'];

和

$uid=$row['user_id'];

代替。

另一方面，查询不是很可读。用明确连接的，而不是那些隐：

SELECT b.book_id,u.user_id,user_name,book_name,review_date,book_rating,review 
FROM tbl_books b 
INNER JOIN tbl_book_reviews br ON b.book_id=br.book_id 
INNER JOIN tbl_user u ON u.user_id=br.user_id 
WHERE moderated='n' 
ORDER BY review_date ASC 
LIMIT 1

这样做的好处是，连接条件是接近被连接的表，而不是在WHERE子句。

来源

2011-04-24 09:54:42 Oswald

谢谢！这一直困扰着我这么久.. :) – yurimano 2011-04-24 10:00:08

选择查询不适用于链接表（mysql）

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