差异是PHP \ SQL返回

Question

所以，我有两个功能：

function display_name1($s){ 
     global $db; 
     $query1 = "SELECT Taken From Alcohol where P_Key = $s"; 
     $r = $db->prepare($query1); 
     $r->execute(); 
     $result = $r->fetchColumn(); 
     return $result; 

} 

    function write_Recipe($s){ 
     global $db; 
     $query1 = "SELECT Taken From Alcohol where Name = $s"; 
     $r = $db->prepare($query1); 
     $r->execute(); 
     $result = $r->fetchColumn(); 
     return $result; 

    } 

唯一的区别是，我在第一个例子匹配输入“$ s”用“p_key的值”和“名”在后者。当我为第一个功能输入数字时，我会得到相应的回报。当我输入一个至少匹配一个“姓名”的字符串时，我什么也收不回来。由于某种原因，它似乎不符合字符串。有任何想法吗？

Answer 1

有一个在SQL查询语法错误。您在第二个查询丢失的表名：

"SELECT Taken From where Name = '$s'" 

应该是这样的：

"SELECT Taken FROM `tablename` WHERE `Name` = '$s'" 

---

另外请注意，如果您已经使用准备好的语句，你应该绑定变量的查询而不是使用字符串连接构建查询。另外使用global对于OOP设计并不完美。这里谈到一个例子怎么能做得更好：

// extend a class from PDO 
class CustomPDO extends PDO { 


    public function display_name($s){ 

     // use placeholder :p_key in query 
     $query1 = "SELECT Taken FROM `Alcohol` WHERE `P_Key` = :p_key"; 
     $r = $this->prepare($query1); 

     // bind value to prepared statement 
     $r->execute(array(
      ':p_key' => $s 
     )); 
     $result = $r->fetchColumn(); 
     return $result; 
    } 

    public function write_recipe($s){ 

     // use placeholder :name in query 
     $query1 = "SELECT Taken FROM `tablename` WHERE `Name` = :name"; 

     // use $this as we are extended from PDO 
     $r = $this->prepare($query1); 

     // bind value to prepared statement 
     $r->execute(array(
      ':name' => $s 
     )); 

     $result = $r->fetchColumn(); 
     return $result; 
    } 
} 

然后使用这个类像一个普通的PDO对象：

$db = new CustomPDO($connection_string, $user, $password); 

但有两个方法：

$result = $db->display_name('foo'); 
$result = $db->write_recipe('foo'); 

Answer 2

当对字符串查询，你应该围绕一个变量加上引号，像这样：

"SELECT Taken From where Name = '$s'"

而且你的第二个查询缺少一个表名。

"SELECT Taken From表名where Name = '$s'"

Answer 3

字符串需要被引用（如果你还没有的话可能会逃脱）。您似乎在使用PDO，为什么不添加占位符？取而代之的是执行execute(array($s));，让PDO为你做好工作？

function display_name1($s){ 
    global $db; 
    $query1 = "SELECT Taken From Alcohol where P_Key = ?"; 
    $r = $db->prepare($query1); 
    $r->execute(array($s)); 
    $result = $r->fetchColumn(); 
    return $result; 
} 

function write_Recipe($s){ 
    global $db; 
    $query1 = "SELECT Taken From Alcohol where Name = ?"; 
    $r = $db->prepare($query1); 
    $r->execute(array($s)); 
    $result = $r->fetchColumn(); 
    return $result; 

}