删除内连接行

Question

我创建了两个表，简单注释和评论者，并将它们连接到INNER JOIN。

• Simplecomments是每个评论者的每一个细节，涉及其评论，reg_date，commentorid等...
• 评论者是评论者的个人信息有下列：ID，姓名，电子邮件..

我已经加入他们成功，但我很难从联合表中删除。

我想使它像这样的逻辑：

1. 如果有一个名为--let评注的最后一行说A--然后同时删除他/她的评论详细信息和他/她自己从桌子上。

2. 否则如果A已评论很多次，有不同的意见，删除了他/她的意见的细节，但让他/她的个人信息仍然因为A有没有其他意见。

这是我如何做了它：

if (!empty($_POST["delete"])) 
{ 
    foreach ($_POST["delete"] as $key => $value) 
    { 
     $resultid = $conn->query("SELECT commentorid FROM `simplecomments` WHERE id=".$value); 
     $rowid = $resultid->fetch_assoc(); 

     $outputdelete = $rowid["name"] . " has been deleted" . "<br>"; 

     $deletedname = $deletedname.$outputdelete; 
     $RES = mysql_num_rows($resultid); 
     $counter = 0; 
      while($row = $RES) 
      { 
       //IF IT'S LAST ROW, DELETE COMMENTOR AND HIS/HER COMMENTDETAILS 
       if(++$counter == $results) { 
        $resultid = $conn->query("DELETE FROM `commentor`"); 
       } 
       //ELSE JUST DELETE HIS/HER COMMENTDETAILS, LET HIS/HER INFO REMAIN 
       else{ 
        $resultid = $conn->query("DELETE FROM `simplecomments` WHERE id=".$value); 
       } 
      } 
    } 

} 

但是代码将无法正常工作。我得到一个错误：

Warning: mysql_num_rows() expects parameter 1 to be resource [..]...

Answer 1

考虑运行DELETE...INNER JOIN和DELETE与子查询条件语句，避免PHP查询获取循环与if/else的逻辑似乎是以下几点：

1. 删除任何评注者的个人资料，如果评论他/她只有一条评论
2. 如果他/她有多个（即多个）评论，则只删除评论者的评论。

是的，所有三个DELETE可以在所有ID上同时运行，因为互斥条件放在前两个和最后一个之间。因此，前两个影响行或最后一个影响每次迭代的行。未受影响的人将从两个表中删除零行。

此外，simplecomments记录首先删除，因为这个表可能与评注外键约束，因为它一个一对多的关系。最后，下面假设评论 ID传递到循环（不是评论或 id）。

PHP（使用参数，假定$ conn是一个mysqli的连接对象）

foreach ($_POST["delete"] as $key => $value) { 

    // DELETE COMMENTS AND THEN PROFILE FOR COMMENTORS WITH ONE POST  
    $sql = "DELETE FROM `simplecomments` s 
      WHERE s.id = ? 
      AND (SELECT COUNT(*) FROM `simplecomments` sub 
        WHERE sub.commentorid = s.commentorid) = 1"; 
    $stmt = $conn->prepare($sql); 
    $stmt->bind_param("i", $value); 
    $stmt->execute(); 
    $stmt->close(); 

    $sql = "DELETE c.* FROM `simplecomments` c 
      INNER JOIN `simplecomments` s ON s.commentorid = c.id 
      WHERE s.id = ? 
      AND (SELECT COUNT(*) FROM `simplecomments` sub 
        WHERE sub.commentorid = s.commentorid) = 1"; 
    $stmt = $conn->prepare($sql); 
    $stmt->bind_param("i", $value); 
    $stmt->execute(); 
    $stmt->close(); 


    // DELETE COMMENTS FOR COMMENTORS WITH MULTIPLE POSTS BUT KEEP PROFILE 
    $sql = "DELETE FROM `simplecomments` s 
      WHERE s.id = ? 
      AND (SELECT COUNT(*) FROM `simplecomments` sub 
        WHERE sub.commentorid = s.commentorid) > 1";  
    $stmt = $conn->prepare($sql); 
    $stmt->bind_param("i", $value); 
    $stmt->execute(); 
    $stmt->close(); 
} 

或者，对于DRY-ER方法中，循环的SQL语句中的阵列：

$sqls = array(
      0 => "DELETE FROM `simplecomments` s WHERE s.id = ? AND (SELECT COUNT(*) FROM `simplecomments` sub WHERE sub.commentorid = s.commentorid) = 1", 
      1 => "DELETE c.* FROM `simplecomments` c INNER JOIN `simplecomments` s ON s.commentorid = c.id WHERE s.id = ? AND (SELECT COUNT(*) FROM `simplecomments` sub WHERE sub.commentorid = s.commentorid) = 1", 
      2 => "DELETE FROM `simplecomments` s WHERE s.id = ? AND (SELECT COUNT(*) FROM `simplecomments` sub WHERE sub.commentorid = s.commentorid) > 1" 
     ); 

foreach ($_POST["delete"] as $key => $value) { 
    foreach($sqls as $sql) { 
     $stmt = $conn->prepare($sql); 
     $stmt->bind_param("i", $value); 
     $stmt->execute(); 
     $stmt->close(); 
    } 
}