子查詢（COUNT）不起作用

Question

我正在使用PHP和MySQL。 此查詢有效，其中我的頁面URL為MySite / Carl_Sagan（Carl_Sagan = $ MyURL），而Carl_Sagan也是數據庫表中名為people的值，字段URL：

$sql= "SELECT COUNT(URL) AS num FROM people WHERE URL = :MyURL";
$stmt = $pdo->prepare($sql);
$stmt->bindParam(':MyURL',$MyURL,PDO::PARAM_STR);
$stmt->execute();
$Total = $stmt->fetch();

switch($Total['num'])
{
case 1:
echo "\n";
require($BaseINC."/$MyPHP/inc/C/2_Child.php");
break;
case 0:
break;
default:
break;
}

但是，當我通過UNION ALL將多個表鏈接在一起，將其轉換為子查詢時，它將不起作用。 我沒有收到任何錯誤消息，但是$ Total ['num']的值為0，應為1。

誰能看到下面發布的我的子查詢的問題？

 $sql = "SELECT SUM(num) FROM (
  SELECT COUNT(URL) AS num FROM pox_topics WHERE URL = :MyURL
  UNION ALL
  SELECT COUNT(URL) AS num FROM people WHERE URL = :MyURL
  UNION ALL
  SELECT COUNT(Taxon) AS num FROM gz_life WHERE Taxon = :MyURL
  ) AS X";
 $stmt = $pdo->prepare($sql);
 $stmt->bindParam(':MyURL',$MyURL,PDO::PARAM_STR);
 $stmt->execute();
 $Total = $stmt->fetch();

我應該注意，即使我將子查詢剝離到原始表中，子查詢也不起作用，如下所示：

$sql = "SELECT SUM(num) FROM (
 SELECT COUNT(URL) AS num FROM people WHERE URL = :MyURL
) AS X";
$stmt = $pdo->prepare($sql);
$stmt->bindParam(':MyURL',$MyURL,PDO::PARAM_STR);
$stmt->execute();
$Total = $stmt->fetch();

Answer 1

沒有$Total['num']了。 嘗試SELECT SUM(num) AS num ...