php – 将LIMIT 1添加到COUNT个查询

$sql = "
SELECT SUM(num) as num FROM (
  SELECT
    COUNT(URL) AS num,'World' AS GoSection,'GW' AS MySite
  FROM gw_geog
  WHERE URL = :MyURL AND G1 = 1
UNION ALL
  SELECT
    COUNT(URL) AS num,'GW' AS MySite
  FROM gw_geog_political
  WHERE URL = :MyURL
 ) AS X";

$stmt = $pdo->prepare($sql);
$stmt->bindParam(':MyURL',$MyURL,PDO::PARAM_STR);
$stmt->execute();
$Total = $stmt->fetch();

我想做两个改变：

1)从每行删除WHERE URL =：MyURL,并将其合并到查询末尾的单行中

2)通过添加LIMIT 1来重复Zap

这就是我现在正在使用的.

$sql = "SELECT SUM(num) as num FROM (
 SELECT COUNT(URL) AS num,'GW' AS MySite FROM gw_geog WHERE URL = :MyURL AND G1 = 1
 UNION ALL
 SELECT COUNT(URL) AS num,'GW' AS MySite FROM gw_geog_political WHERE URL = :MyURL
 ) AS X
WHERE X.URL LIKE :MyURL LIMIT 1";
$stmt = $pdo->prepare($sql);
$stmt->bindParam(':MyURL',PDO::PARAM_STR);
$stmt->execute();
$Total = $stmt->fetch();

但是,我收到错误消息Unknown column X.SUM(或X.URL等).

有人能告诉我这样做的正确方法吗？