Sql 联合查询未显示第二次查询的记录

我有以下SQL查询：

select (case when len(GroupName) = 0 then 'Unknown' else GroupName end) as GroupName 
,PaperId,Color,Duplex, sum(Page_Printed) As A3PagesPrinted, sum(Cost) as A3TotalCost 
from printstat where paperid = 8 and color = 0 and duplex = 0 
and Date_Print >= '2013-01-01' and Date_Print < '2013-10-21'
group by GroupName, PaperId, Color, Duplex

union all

select (case when len(GroupName) = 0 then 'Unknown' else GroupName end) as GroupName
,PaperId,Color,Duplex, sum(Page_Printed) As A3DuplexPagesPrinted, 
sum(Cost) as A3DuplexTotalCost from printstat where paperid = 8 and color = 0 
and duplex = 1 and Date_Print >= '2013-01-01' and Date_Print < '2013-10-21'
group by GroupName, PaperId, Color, Duplex

现在，两个查询在单独运行时都返回值。但当我同时执行它们时，第二个查询的记录显示为一个DuplexPageSprint和一个DuplexTotalCost

为什么会这样？

联合查询将从查询的第一部分获取列名，并以相同的顺序将所有后续部分填充到这些列中，而不考虑名称或别名

因此，第二部分中的第五列和第六列（别名A3DuplexPagesPrinted和A3DuplexTotalCost）将填入结果的第五列和第六列，并命名为A3PagesPrinted和A3TotalCost（别名来自第一个SELECT子句）

如果要区分两个查询中的列，则必须为查询的每个部分指定所有列注意下面的空值：

select case when len(GroupName) = 0 then 'Unknown' else GroupName end as GroupName,
    PaperId,
    Color,
    Duplex, 
    sum(Page_Printed) As A3PagesPrinted, 
    sum(Cost) as A3TotalCost,
    NULL AS A3DuplexPagesPrinted,
    NULL AS A3DuplexTotalCost
from printstat where paperid = 8 and color = 0 and duplex = 0 
and Date_Print >= '2013-01-01' and Date_Print < '2013-10-21'
group by GroupName, PaperId, Color, Duplex

union all

select case when len(GroupName) = 0 then 'Unknown' else GroupName end as GroupName,
    PaperId,
    Color,
    Duplex,
    NULL,
    NULL,
    sum(Page_Printed) As A3DuplexPagesPrinted, 
    sum(Cost) as A3DuplexTotalCost
from printstat where paperid = 8 and color = 0 
and duplex = 1 and Date_Print >= '2013-01-01' and Date_Print < '2013-10-21'
group by GroupName, PaperId, Color, Duplex

---

实际上，我的表不包含A3PageSprint A3TotalCost A3DuplexPageSprint A3DuplexTotalCost列。这些是基于where子句中定义的条件的用户定义的列。这很好，但如果您希望将数据分隔开，则必须指定所有跨行的列。我假设这是动态生成的SQL