Question

给出以下查询

Select Count(*) From TableA

Select Count(*) From TableB

Select Count(*) From TableC

Select Count(*) From TableD

我想返回如下视图：

-----------
| Counts  |
-----------
| 2       | --from TableA
-----------
| 3       | --from TableB
----------
| 4       | --from TableC
----------
| 5       | --from TableD
----------

我尝试使用UNION，例如：

CREATE VIEW [Foo]
AS
SELECT COUNT(*) AS [Counts]
FROM TableA
UNION
SELECT COUNT(*)
FROM TableB
UNION
SELECT COUNT(*)
FROM TableC
UNION
SELECT COUNT(*)
FROM TableD

但是订单不正确

-----------
| Counts  |
-----------
| 2       | --from TableA
-----------
| 3       | --from TableB
----------
| 5       | --from TableD
----------
| 4       | --from TableC
----------

除了UNION之外，还有其他替代方法可以用来生成所需的结果集吗？

Answer 1

非常接近，只需为您的订单添加一个派生字段。

CREATE VIEW [Foo]
AS
SELECT TOP(100) PERCENT
*
FROM
(
    SELECT COUNT(*) AS [Counts], RowOrder=1
    FROM TableA
    UNION
    SELECT COUNT(*), 2
    FROM TableB
    UNION
    SELECT COUNT(*), 3
    FROM TableC
    UNION
    SELECT COUNT(*), 4
    FROM TableD
)AS X
ORDER BY RowOrder

OR-订单在计数视图之外。

CREATE VIEW [Foo]
AS
SELECT 
*
FROM
(
    SELECT COUNT(*) AS [Counts], RowOrder=1
    FROM TableA
    UNION
    SELECT COUNT(*), 2
    FROM TableB
    UNION
    SELECT COUNT(*), 3
    FROM TableC
    UNION
    SELECT COUNT(*), 4
    FROM TableD
)AS X

...
SELECT * FROM Foo ORDER BY RowOrder

Answer 2

UNION内部为您进行排序，您需要union all或定义显式排序：

SELECT COUNT(*) AS [Counts]
FROM TableA UNION ALL
SELECT COUNT(*)
FROM TableB UNION ALL
SELECT COUNT(*)
FROM TableC UNION ALL
SELECT COUNT(*)
FROM TableD;

您还可以定义显式顺序：

SELECT COUNT(*) AS [Counts], 1 as SortOrder
FROM TableA UNION 
SELECT COUNT(*), 2
FROM TableB UNION 
SELECT COUNT(*), 3
FROM TableC UNION 
SELECT COUNT(*), 4
FROM TableD;

因此，您需要在视图order by中使用Foo子句

select f.*
from Foo f
order by SortOrder;

Answer 3

视图返回无序结果集。您可以尝试做：

create view v_counts as
    select . . .
    order by . . .

您将收到错误消息：

除非还指定了TOP，OFFSET或FOR XML，否则ORDER BY子句在视图，内联函数，派生表，子查询和公用表表达式中无效。

正如消息所暗示的那样，有一种方法可以解决这个问题，但我建议不要这样做-即使您作弊，也不能保证视图会按顺序返回结果。 / p>

相反，请添加表名称：

Select 'TableA' as which, Count(*) From TableA union all Select 'TableB' as which, Count(*) From TableB union all Select 'TableC' as which, Count(*) From TableC union all Select 'TableD' as which, Count(*) From TableD;

SQL Server-使用来自多个结果集的行创建视图

3 个答案: