UNION与两个带有大WHERE子句的查询

我有两个几乎相同的查询—一个连接表gz_life_groups和gz_life_groups2，另一个连接表gz_life_floters和gz_life_floaters2。我想使用UNION将两个查询合并为一个查询，但是我还没有能够跳过所有的环节。

简单解释一下这些表的作用:想象一下导航到URL MySite/life/ursus-maritimus。Ursus-maritimus匹配数据库表字段Taxon中的值。因此，如果Ursus maritimus(北极熊)被放在一个名为"白色哺乳动物"的组中，它将匹配字段Title("白色哺乳动物")和URL("白色哺乳动物")中表gz_life_groups中的值。字段Links仅包含到相关页面的链接。

$Groups = $pdo->prepare("SELECT G2.URL, G2.Taxon, G1.URL, G1.Title, G1.Links
 FROM gz_life_groups2 AS G2
 LEFT JOIN gz_life_groups G1 ON G1.URL = G2.URL
 WHERE Taxon = :Kingdom AND G2.Live = '1'
 OR Taxon = :Phylum AND G2.Live = '1'
 OR Taxon = :Class AND G2.Live = '1'
 OR Taxon = :Order AND G2.Live = '1'
 OR Taxon = :Family AND G2.Live = '1'
 OR Taxon = :Genus AND G2.Live = '1'
 OR Taxon = :MyURL AND G2.Live = '1'
 GROUP BY G1.URL
 Order By G2.N");
$Groups->execute(array(
 'Kingdom'=>$Kingdom,
 'Phylum'=>$Phylum,
 'Class'=>$Class,
 'Order'=>$Order,
 'Family'=>$Family,
 'Genus'=>$Genus,
 'MyURL'=>$MyURL
));

$Names = $pdo->prepare("SELECT F2.URL, F2.Taxon, F1.URL, F1.Name, F1.Parent
 FROM gz_life_floaters2 AS F2
 LEFT JOIN gz_life_floaters F1 ON F1.URL = F2.URL
 WHERE Taxon = :Kingdom AND F2.Live = '1'
 OR Taxon = :Phylum AND F2.Live = '1'
 OR Taxon = :Class AND F2.Live = '1'
 OR Taxon = :Order AND F2.Live = '1'
 OR Taxon = :Family AND F2.Live = '1'
 OR Taxon = :Genus AND F2.Live = '1'
 OR Taxon = :MyURL AND F2.Live = '1'
 GROUP BY F1.URL
 Order By F2.N");
$Names->execute(array(
 'Kingdom'=>$Kingdom,
 'Phylum'=>$Phylum,
 'Class'=>$Class,
 'Order'=>$Order,
 'Family'=>$Family,
 'Genus'=>$Genus,
 'MyURL'=>$MyURL
));

这就是我对UNION有限的了解。我不知道如何添加连接或WHERE子句…

$stm = $pdo->prepare("SELECT *
 FROM (
 SELECT G2.URL, G2.Taxon, G1.URL, G1.Title, NULL AS Parent, G1.Links
 FROM gz_life_groups2 AS G2
 UNION ALL 
 SELECT F2.URL, F2.Taxon, F1.URL, F1.Name AS Title, F1.Parent, NULL AS Links
 FROM gz_life_floaters2 AS F2
) AS Combined
 WHERE Combined.URL LIKE :MyURL");
$stm->execute(array(
'MyURL'=>$MyURL
));