Aggregating Data with MAX & GROUP BY in VIEWS with a WHERE restriction - tsql

Question

Here is my Request.
Our Application generates a statement which invokes a view in a SQL-Server DB.
This statement selects DISTINCT or GROUP BY Data-fields from the view
passing a restricted subset of IDs.
Background:
I am using SQL-Server 2008 R2 running on Windows Server 2008 R2
With an example-table I will try to explain the problem.
Given this example table: [TabA]
ID [INT] DATA [VARCHAR(8)]
--- ----
51 A1
50 A1
110 A5
100 A5
We then create the following view:
CREATE VIEW ViewOnTabA
AS
SELECT
MAX(ta.ID) As ID, ta.DATA
FROM
TabA ta
GROUP BY ta.DATA
GO
With this statement, generated by our application,
we call the view passing some ID values:
SELECT
ID, DATA
FROM ViewOnTabA
WHERE ID in (51,50,110,100)
The result is Ok
The Data fields are grouped and complete:
ID DATA
-- ----
51 A1
110 A5
If instead of all IDs we pass only the smaller ID number: (50 instead of 51)
...
WHERE ID in (50,110,100)
The result is incomplete (ID 50 is missing):
ID DATA
-- ----
110 A5
But we expected
ID DATA
-- ----
50 A1
110 A5
It seems that in a VIEW the GROUP BY is executing before the WHERE condition.
As we cannot invoke stored procedures from our application,
we have to rely on calling a view.
Are there other possibilities to have a DISTINCT or GROUP BY order
of the DATA fields (in the example) within a VIEW.
The ID-fields must not necessarily be filtered with the MAX aggregate function.
But the Where restriction has to be applied on them.
P.S.
Executing this Select in a normal query including
the (WHERE ID in ...) restriction it works fine:
SELECT
MAX(ta.ID) As ID, ta.DATA
FROM
TabA ta
WHERE ID in (50,110,100)
GROUP BY ta.DATA
output>>>>
ID DATA
-- ----
50 A1
110 A5
For simulating this example
here are the create & insert statements:
create table TabA
(
ID int ,
DATA varchar(8)
)
go
insert into TabA values (51,'A1')
insert into TabA values (50,'A1')
insert into TabA values (110,'A5')
insert into TabA values (100,'A5')
Any help would be greatly appreciated.
Regards,
Alberto

Answer 1

For this to work the way that you are expecting to, you would need to remove the group by from your view. The reason why you are not seeing for e.g. the "50" in your results, is because it is already filtered out by the group by in the view.
You will either need to change your view (if nothing else is using it), or create a new view like this:
CREATE VIEW ViewOnTabA /* or use a new name */
AS
SELECT ta.ID, ta.DATA
FROM TabA ta
GO
... and then run the select statement with the where clause on this view.
SELECT
MAX(ta.ID) As ID, ta.DATA
FROM
ViewOnTabA ta /* or use the new view's name */
WHERE ta.ID in (50,110,100)
GROUP BY ta.DATA