把一個PHP變量在SQL查詢

Question

我有以下代碼：

try 
{ 
    $sql = 'SELECT id, type, date, amount, description, category 
FROM `transactions` 
    WHERE type = "income" 
    AND month(date) = '$monthselect' 
    ORDER BY `transactions`.`id` DESC 
    LIMIT 0,50'; 
    $result2 = $pdo->query($sql); 
} 

現在，我想給這個month(Date)我想選擇哪個月份的變量。如果我放1，它會給我一月。所以我想，如果我用1定義一個變量，我可以用它來選擇一個月，對吧？

​​

它不工作。我究竟做錯了什麼？

Answer 1

使用預處理語句：

$stm = $pdo->prepare('SELECT id, type, date, amount, description, category 
FROM `transactions` 
    WHERE type = "income" 
    AND month(date) = ? 
    ORDER BY `transactions`.`id` DESC 
    LIMIT 0,50'); 

$stm->execute(compact('monthselect')); 
$result2 = $stm->fetchAll(); 

既然你不能在查詢中加「1」直接，我在這裏假設變量來自用戶的輸入。

Answer 2

要連接在PHP中，你需要使用字符串。運營商。

$sql = 'SELECT id, type, date, amount, description, category 
    FROM `transactions` 
    WHERE type = "income" 
    AND month(date) = ' . $monthselect . ' 
    ORDER BY `transactions`.`id` DESC 
    LIMIT 0,50'; 

Answer 3

我會經常使用雙引號在PHP替代變量：

$sql = "SELECT id, type, date, amount, description, category 
    FROM `transactions` 
    WHERE type = 'income' 
    AND month(date) = $monthselect 
    ORDER BY `transactions`.`id` DESC 
    LIMIT 0,50"; 

請注意，您需要將現有雙引號（字符串內）交換到單引號。你也可以逃避它們，但是我發現這種方式使它更具可讀性。

Answer 4

你的問題是，你要使用單引號裏面的變量，在其內部的PHP沒有被翻譯

我覺得用在我的查詢雙引號它讓我不僅使用變量在其中，但也可以在傳遞給db的值周圍使用單引號mark

$sql = "SELECT id, type, date, amount, description, category 
FROM `transactions` 
WHERE type = 'income' 
AND month(date) = $monthselect 
ORDER BY `transactions`.`id` DESC 
LIMIT 0,50";