[英]Add Identity column to a view in SQL Server 2008
This is my view:这是我的观点:
Create View [MyView] as
(
Select col1, col2, col3 From Table1
UnionAll
Select col1, col2, col3 From Table2
)
I need to add a new column named Id
and I need to this column be unique so I think to add new column as identity.我需要添加一个名为Id
的新列,我需要这个列是唯一的,所以我想添加新列作为身份。 I must mention this view returned a large of data so I need a way with good performance, And also I use two select query with union all I think this might be some complicated so what is your suggestion?我必须提到这个视图返回了大量数据,所以我需要一种具有良好性能的方法,而且我使用两个带有联合的选择查询,我认为这可能有些复杂,所以你的建议是什么?
Use the ROW_NUMBER()
function in SQL Server 2008.在 SQL Server 2008 中使用ROW_NUMBER()
函数。
Create View [MyView] as
SELECT ROW_NUMBER() OVER( ORDER BY col1 ) AS id, col1, col2, col3
FROM(
Select col1, col2, col3 From Table1
Union All
Select col1, col2, col3 From Table2 ) AS MyResults
GO
The view is just a stored query that does not contain the data itself so you can add a stable ID.该视图只是一个不包含数据本身的存储查询,因此您可以添加一个稳定的 ID。 If you need an id for other purposes like paging for example, you can do something like this:如果您需要一个 id 用于其他目的,例如分页,您可以执行以下操作:
create view MyView as
(
select row_number() over ( order by col1) as ID, col1 from (
Select col1 From Table1
Union All
Select col1 From Table2
) a
)
There is no guarantee that the rows returned by a query using ROW_NUMBER() will be ordered exactly the same with each execution unless the following conditions are true:除非满足以下条件,否则无法保证使用 ROW_NUMBER() 的查询返回的行在每次执行时的排序完全相同:
There is a secondary issue here, with this being a view.这里有一个次要问题,这是一个观点。 Order By's don't always work in views (long-time sql bug). Order By 并不总是在视图中工作(长期的 sql 错误)。 Ignoring the row_number() for a second:暂时忽略 row_number() :
create view MyView as
(
select top 10000000 [or top 99.9999999 Percent] col1
from (
Select col1 From Table1
Union All
Select col1 From Table2
) a order by col1
)
Using "row_number() over ( order by col1) as ID" is very expensive.使用“row_number() over (order by col1) as ID”是非常昂贵的。 This way is much more efficient in cost:这种方式在成本上更有效:
Create View [MyView] as
(
Select ID = isnull(cast(newid() as varchar(40)), '')
, col1
, col2
, col3
From Table1
UnionAll
Select ID = isnull(cast(newid() as varchar(40)), '')
, col1
, col2
, col3
From Table2
)
use ROW_NUMBER() with "order by (select null)" this will be less expensive and will get your result.将 ROW_NUMBER() 与“order by (select null)”一起使用,这样成本会更低,并且会得到您的结果。
Create View [MyView] as
SELECT ROW_NUMBER() over (order by (select null)) as id, *
FROM(
Select col1, col2, col3 From Table1
Union All
Select col1, col2, col3 From Table2 ) R
GO
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