差異是PHP \ SQL返回

Question

所以，我有兩個功能：

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; 

    } 

唯一的區別是，我在第一個例子匹配輸入「$ s」用「p_key的值」和「名」在後者。當我爲第一個功能輸入數字時，我會得到相應的回報。當我輸入一個至少匹配一個「姓名」的字符串時，我什麼也收不回來。由於某種原因，它似乎不符合字符串。有任何想法嗎？

Answer 1

有一個在SQL查詢語法錯誤。您在第二個查詢丟失的表名：

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

應該是這樣的：

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

---

另外請注意，如果您已經使用準備好的語句，你應該綁定變量的查詢而不是使用字符串連接構建查詢。另外使用global對於OOP設計並不完美。這裏談到一個例子怎麼能做得更好：

// 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; 
    } 
} 

然後使用這個類像一個普通的PDO對象：

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

但有兩個方法：

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

Answer 2

當對字符串查詢，你應該圍繞一個變量加上引號，像這樣：

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

而且你的第二個查詢缺少一個表名。

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

Answer 3

字符串需要被引用（如果你還沒有的話可能會逃脫）。您似乎在使用PDO，爲什麼不添加佔位符？取而代之的是執行execute(array($s));，讓PDO爲你做好工作？

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; 

}