I have a problem about storing multiple categorical data. One category can have any size of cascade depth. I think it is not good idea to create more tables with relationships. What is the best way of storing this kind of categorical data.
ex categories:
-MainCategory1
-subcategory1
-subcategory11
-subcategory12
-subcategory13
--subcategory131
-subcategory2
-subcategory21
-subcategory22
-subcategory221
-subcategory23
-subcategory231
-subcategory2311
-MainCategory2
-subcategory21
-subcategory211
-subcategory2131
-subcategory2131
-subcategory212
-subcategory213
-subcategory2131
One common practice would be to create a single table where each category has an id, a name and a parent id (with top categories having parent id of null):
CREATE TABLE categories (
id NUMERIC PRIMARY KEY,
name VARCHAR(100),
parent_id NUMERIC FOREIGN KEY REFERENCES categories(Id)
)
Some of your data, e.g., would look like this:
INSERT INTO categories VALUES (1, 'MainCategory1', null);
INSERT INTO categories VALUES (2, 'subcategory1', 1);
You need to define parent child structure
CREATE TABLE CATEGORIES (ID INT, PARENT_ID INT, NAME VARCHAR)
then you select categories that have no PARENT_ID
SELECT * FROM CATEGORIES WHERE PARENT_ID IS NULL
they are masters and then on each layer you select
SELECT C.* FROM CATEGORIES C
INNER JOIN CATEGORIES C1 ON C1.PARENT_ID = C.ID
to get children of current record.
And then insert into categories
INSERT INTO CATEGORIES
SELECT 1, NULL, 'MainCategory1'
UNION ALL SELECT 10, 1, 'subcategory1'
UNION ALL SELECT 11, 10, 'subcategory11'
UNION ALL SELECT 12, 10, 'subcategory12'
UNION ALL SELECT 13, 10, 'subcategory13'
UNION ALL SELECT 131, 13, 'subcategory131'
UNION ALL SELECT 2, 1, 'subcategory2'
-- ...AND SO ON
SQL Server implements the hierarchyid data type.
You should consider using that.
http://msdn.microsoft.com/en-us/library/bb677173.aspx
This is a long-standing issue with using a relational database to contain hierarchical data. Generally it was done using self-referencing tables but that has always been an absolute bear to work with. I always find it somewhat fitting that the designer of Java noticed that the best hierarchical database in common use was the directory structure of the disks. So that's what Java uses!
Many DBMSs have enhancements to make working with hierarchical data easier. They work (or not) with varying degrees of success and difficulty for the developer. One method I recently worked out as a response to a question here at SO can be seen here. It's not complete. But actions such as moving a node or entire subtree from one place to another would just be a mathematical operation, not readjusting FK pointers.
Related
SQL Server Gurus ...
Currently using MS SQL Server 2016
I know Joe Celko and all SQL purists are squirming at the thought of using bitmasks, but I have a use case in which I need to query for all widgets that contain a set of given attributes.
Each widget may contain several hundred attributes.
The attributes of a widget are either present or not (1 = present, 0 = not
present)
One way I thought to do this is via bitmasks – the attributes to be found (a bitmask) could be ANDed with the attributes of each widget to find matches in a single operation. For example, the widgets table might be:
widets table:
widget_uid Uniqueidentifier
attributes BigInt
SELECT widget_uid
FROM widgets
WHERE ( attributes & bitmask ) = bitmask;
Problem is, using a BigInt for the attributes limits the number of attributes to 64 (a widget can have several hundred attributes), I could group the attributes in chunks of 64 bits, ie:
widets table:
widget_uid Uniqueidentifier
attributes0 BigInt -- Attributes 0-63
attributes1 BigInt -- Attributes 64-127
attributes2 BigInt -- Attributes 128-191
SELECT widget_uid
FROM widgets
WHERE ( attributes0 & bitmask0 ) = bitmask0
AND ( attributes1 & bitmask1 ) = bitmask1
AND ( attributes2 & bitmask2 ) = bitmask2
... but was wondering if anyone has come up with a solution for bit operations using bitmasks with greater than 64 bits – or if other (more efficient?) solutions would exist?
In the use case, the widgets table does contain other columns, but I am only concerned with the attributes matching portion of the query at the moment.
Any and all ideas are welcome - would be interested in knowing how others tackle this particular problem.
Thanks in advance.
We had a similar use case, on a significantly large data set. This was for an e-commerce site with products and attributes. Our case was a bit more complex than here, where we had any possible number of attributes and then values assigned to those attributes. e.g. Color - Red/Green/Blue, Size - S/M/L etc.
We found that associated tables with good indexing was the key in our case. While this may not be an option for you we found this to be the optimal solution for a dynamic data set.
I can code you up an example if you feel it will be helpful.
Edited to add example:
DROP TABLE IF EXISTS #Widgets
DROP TABLE IF EXISTS #Attributes
DROP TABLE IF EXISTS #WidgetAttributes
CREATE TABLE #Widgets (widget_UID UNIQUEIDENTIFIER PRIMARY KEY CLUSTERED, Name NVARCHAR(255))
CREATE TABLE #Attributes (Attribute_UID UNIQUEIDENTIFIER PRIMARY KEY CLUSTERED, Name NVARCHAR(255))
CREATE TABLE #WidgetAttributes (widget_UID UNIQUEIDENTIFIER,Attribute_UID UNIQUEIDENTIFIER)
CREATE NONCLUSTERED INDEX ix_WidgetAttribute ON #WidgetAttributes (Attribute_UID) INCLUDE (widget_UID)
INSERT INTO #Widgets (widget_UID, Name) values
( '{c63bea73-2331-4698-82c9-f71845ab8601}', N'Widget 1' ),
( '{a0865b8f-606b-4273-9207-39a8a26016c4}', N'Widget 2' ),
( '{211fe27e-ab98-4b61-83a3-3d006d66db5a}', N'Widget 3' )
INSERT INTO #Attributes (Attribute_UID, Name)
VALUES
( '{99354dc0-d0b2-4919-a887-edf115eeb1bd}', N'Height' ),
( '{136bbe4c-497d-472f-a905-670e4a7805d0}', N'Width' ),
( '{f006f950-30d1-453e-8e09-4f7d140fa3cb}', N'Depth' ),
( '{0d190639-677f-4b75-8d36-1bdac00de132}', N'Colour' )
-- Set links
-- Widget 1 All attributes
-- Widget 2 Height Width
-- Widget 3 Colour
INSERT INTO #WidgetAttributes (widget_UID, Attribute_UID)
SELECT '{c63bea73-2331-4698-82c9-f71845ab8601}',Attribute_UID FROM #Attributes
UNION ALL
SELECT TOP (2) '{a0865b8f-606b-4273-9207-39a8a26016c4}',Attribute_UID FROM #Attributes WHERE Name<> 'Colour'
UNION ALL
SELECT '{211fe27e-ab98-4b61-83a3-3d006d66db5a}',Attribute_UID FROM #Attributes WHERE Name = 'Colour'
-- #SearchAttributes to hold list of attributes you are trying to find
DECLARE #SearchAttributes TABLE (Attribute_UID UNIQUEIDENTIFIER)
INSERT INTO #SearchAttributes
SELECT Attribute_UID FROM #Attributes WHERE Name<> 'Colour'
;WITH cte AS (
SELECT WA.widget_UID, COUNT(1) AttributesPresent FROM #WidgetAttributes WA
JOIN #SearchAttributes SA ON SA.Attribute_UID = WA.Attribute_UID
GROUP BY WA.widget_UID
)
SELECT cte.AttributesPresent
, W.widget_UID
, W.Name
FROM cte
JOIN #Widgets W ON W.widget_UID = cte.widget_UID
ORDER BY cte.AttributesPresent DESC
Gives an output of:
AttributesPresent widget_UID Name
----------------- ------------------------------------ ----------
3 C63BEA73-2331-4698-82C9-F71845AB8601 Widget 1
2 A0865B8F-606B-4273-9207-39A8A26016C4 Widget 2
We used an approach of counting how many attributes were present for each so we not only had the option of "exact match" but also "closest fit".
Using bitmask in databases is wrong approach. Even if you somewhow manage it to work, you will not be able to use indexes to speed up execution.
Use standard solution, this is standard situation. There is standard M:N relationship between Widgets and Attributes (both should be tables, of course). You will add another table that will assign Attributes to Widgets - you can call it WidgetAttributes.
It will have 3 columns: Id, WidgetId, AttributeId
Then you can simply for example get list of Widgets that have Attribute:
select w.*
from Widgets w
inner join WidgetAttributes wa on wa.WidgetId = w.Id
inner join Attributes a on a.Id = wa.AttributeId
where a.AttributeName='xxx'
I am working on a search filter for a website that will help users find a venue(for get-togethers and ceremonies) that meets their needs. Filters would include such things as: style, amenities, event type, etc. Multiple options in a category can apply to a venue, so a user can select multiple options from style, amenities and event type categories when searching.
My issue is in how I should approach the table design in the database. Currently I have a Venue table with a unique id and basic information, and a number of tables representing each category (style, amenities, etc) where they contain an id and name field.
I know that I need an intermediary table to hold foreign keys, so each option applicable to a category is associated to the venue.
Option 1: Create for each category table a many to many intermediary table with foreign keys to that category and the venue.
Option 2: Create one large intermediary table with foreign keys for every category, as well as the Venue
i.e.
fk_venue
fk_style
fk_amenities
...
I am trying to decide what is more efficient and less of a problem in coding for. Option 1 would require a query to each table which may become complicated to work with, where as option 2 seems easier to query but might have a much larger number of records to handle a venue with many amenities AND event types for example.
This doesn't seem like a new problem but I have had trouble finding resources that detail how best to approach this. We are currently using MSSQL for the DB and are building the site using .net core.
Go with option one. Create a join table to record the many-to-many relationships of each available feature of a venue. Option 2 is very wasteful in terms of storage. Consider a case where you have a venue with only one amenity, when 50 amenities types are available. Also, as I understand what you are suggesting for option 2, you would have to update your database design each time you add an amenity, event_type, or style. That would be a very difficult thing support wise.
In the case of Option 1, some of the tables would be:
Table Name: venue_amenities
Columns: venue_id, amenity_id
Table Name: venue_event_types
Columns: venue_id, event_type_id
Table Name: venue_styles
Columns: venue_id, style_id
When you query everything with a filter, you could query it like:
select distinct
v.venue_id
from venues v
inner join venue_amenities va on v.venue_id = va.venue_id
inner join venue_event_types vet on v.venue_id = vet.venue_id
inner join venue_styles vs on v.venue_id = vs.venue_id
where va.amenity_id in ([selected amenities])
and vet.event_type_id in ([selected event types])
and vs.venue_style in ([selected styles])
Option 3: You could start out with a meta data design. This would allow you to have multiple records per item or entity.
Often these things evolve with the development of tasks, or the evolution of the process and learning the data or the customer understanding some of the finer details that are drawn out as time goes on.
I've seen similar things where people design for hashtags or white lists, searching for that might get you closer to what you are looking for. Here is a working example to get you started.
declare #venue as table(
VenueID int identity(1,1) not null primary key clustered
, Name_ nvarchar(255) not null
, Address_ nvarchar(255) null
);
declare #venueType as table (
VenueTypeID int identity(1,1) not null primary key clustered
, VenueType nvarchar(255) not null
);
declare #venueStuff as table (
VenueStuffID int identity(1,1) not null primary key clustered
, VenueID int not null -- constraint back to venueid
, VenueTypeID int not null -- constraint to dim or lookup table for ... attribute types
, AttributeValue nvarchar(255) not null
);
insert into #venue (Name_)
select 'Bob''s Funhouse'
insert into #venueStuff (VenueID, VenueTypeID, AttributeValue)
select 1, 1, 'Scarrrrry' union all
select 1, 2, 'Food Avaliable' union all
select 1, 3, 'Game tables provided' union all
select 1, 4, 'Creepy';
insert into #venueType (VenueType)
select 'Haunted House Theme' union all
select 'Gaming' union all
select 'Concessions' union all
select 'post apocalyptic';
select a.Name_
, b.AttributeValue
, c.VenueType
from #venue a
join #venueStuff b
on a.VenueID = b.VenueID
join #venueType c
on c.VenueTypeID = b.VenueTypeID
Suppose I have the following parent/child table relationship in my database:
TABLE offer_master( offer_id int primary key, ..., scope varchar )
TABLE offer_detail( offer_detail_id int primary key, offer_id int foreign key, customer_id int, ... )
where offer_master.scope can take on the value
INDIVIDUAL: when the offer is to made to particular customers. In this case,
whenever a row is inserted into offer_master, a corresponding row is
added to offer_detail for each customer to which the offer has been extended.
e.g.
INSERT INTO offer_master( 1, ..., 'INDIVIDUAL' );
INSERT INTO offer_detail( offer_detail_id, offer_id, customer_id, ... )
VALUES ( 1, 1, 100, ... )
INSERT INTO offer_detail( offer_detail_id, offer_id, customer_id, ... )
VALUES ( 2, 1, 101, ... )
GLOBAL: when the offer is made to all customers. In this case,
new offers can be added to the parent table as follows:
INSERT INTO offer_master( 2, ..., 'GLOBAL' );
INSERT INTO offer_master( 3, ..., 'GLOBAL' );
but a child row is added to offer_detail only
when a customer indicates some interest in the offer. So
it may be the case that, at some later point we will have
INSERT INTO offer_detail( offer_detail_id, offer_id, customer_id, ... )
VALUES ( 4, 3, 100, ... )
Given this situation, suppose we would like to query the database
to obtain all offers which have been extended to customer 100;
this includes 3 types of offers:
offers which have been extended specifically to customer 100.
global offers which customer 100 showed no interest in.
global offers which customer 100 did show interest in.
I see two approaches:
Using a Subquery:
SELECT *
FROM offer_master
WHERE offer_id in (
SELECT offer_id
FROM offer_detail
WHERE customer_id = 100 )
OR scope = 'GLOBAL'
Using a UNION
SELECT om.*
FROM offer_master om INNER JOIN
offer_detail od
ON om.offer_id = od.offer_id
WHERE od.customer_id = 100
UNION
SELECT *
FROM offer_master
WHERE scope = 'GLOBAL'
Note: a UNION ALL cannot be used since a global offer
which a customer has shown interest in would be duplicated.
My question is:
Does this query pattern have a name?
Which of the two query methods are preferable?
Should the database design be improved in some way?
I'm not aware of a pattern name.
To me, the second query is clearer but I think either is OK.
offer_detail seems to be a dual purpose table which is a bit of a red flag to me. You might have separate tables for the customers in an individual offer, and the customers who have expressed interest.
this is one on my database tables template.
Id int PK
Title nvarchar(10) unique
ParentId int
This is my question.Is there a problem if i create a relation between "Id" and "ParentId" columns?
(I mean create a relation between a table to itself)
I need some advices about problems that may occur during insert or updater or delete operations at developing step.thanks
You can perfectly join the table with it self.
You should be aware, however, that your design allows you to have multiple levels of hierarchy. Since you are using SQL Server (assuming 2005 or higher), you can have a recursive CTE get your tree structure.
Proof of concept preparation:
declare #YourTable table (id int, parentid int, title varchar(20))
insert into #YourTable values
(1,null, 'root'),
(2,1, 'something'),
(3,1, 'in the way'),
(4,1, 'she moves'),
(5,3, ''),
(6,null, 'I don''t know'),
(7,6, 'Stick around');
Query 1 - Node Levels:
with cte as (
select Id, ParentId, Title, 1 level
from #YourTable where ParentId is null
union all
select yt.Id, yt.ParentId, yt.Title, cte.level + 1
from #YourTable yt inner join cte on cte.Id = yt.ParentId
)
select cte.*
from cte
order by level, id, Title
No, you can do self join in your table, there will not be any problem. Are you talking which types of problems in insert, update, delete operation ? You can check some conditions like ParentId exists before adding new record, or you can check it any child exist while deleting parent.
You can do self join like :
select t1.Title, t2.Title as 'ParentName'
from table t1
left join table t2
on t1.ParentId = t2.Id
You've got plenty of good answers here. One other thing to consider is referential integrity. You can have a foreign key on a table that points to another column in the same table. Observe:
CREATE TABLE tempdb.dbo.t
(
Id INT NOT NULL ,
CONSTRAINT PK_t PRIMARY KEY CLUSTERED ( Id ) ,
ParentId INT NULL ,
CONSTRAINT FK_ParentId FOREIGN KEY ( ParentId ) REFERENCES tempdb.dbo.t ( Id )
)
By doing this, you ensure that you're not going to get garbage in the ParentId column.
Its called Self Join and it can be added to a table as in following example
select e1.emp_name 'manager',e2.emp_name 'employee'
from employees e1 join employees e2
on e1.emp_id=e2.emp_manager_id
I have seen this done without errors before on a table for menu hierarchy you shouldnt have any issues providing your insert / update / delete queries are well written.
For instance when you insert check a parent id exists, when you delete check you delete all children too if this action is appropriate or do not allow deletion of items that have children.
It is fine to do this (it's a not uncommon pattern). You must ensure that you are adding a child record to a parent record that actually exists etc., but there's noting different here from any other constraint.
You may want to look at recursive common table expressions:
http://msdn.microsoft.com/en-us/library/ms186243.aspx
As a way of querying an entire 'tree' of records.
This is not a problem, as this is a relationship that's common in real life. If you do not have a parent (which happens at the top level), you need to keep this field "null", only then do update and delete propagation work properly.
I have a SQL-Server 2008 database and a schema which uses foreign key constraints to enforce referential integrity. Works as intended. Now the user creates views on the original tables to work on subsets of the data only. My problem is that filtering certain datasets in some tables but not in others will violate the foreign key constraints.
Imagine two tables "one" and "two". "one" contains just an id column with values 1,2,3. "Two" references "one". Now you create views on both tables. The view for table "two" doesn't filter anything while the view for table "one" removes all rows but the first. You'll end up with entries in the second view that point nowhere.
Is there any way to avoid this? Can you have foreign key constraints between views?
Some Clarification in response to some of the comments:
I'm aware that the underlying constraints will ensure integrity of the data even when inserting through the views. My problem lies with the statements consuming the views. Those statements have been written with the original tables in mind and assume certain joins cannot fail. This assumption is always valid when working with the tables - but views potentially break it.
Joining/checking all constraints when creating the views in the first place is annyoing because of the large number of referencing tables. Thus I was hoping to avoid that.
I love your question. It screams of familiarity with the Query Optimizer, and how it can see that some joins are redundant if they serve no purpose, or if it can simplify something knowing that there is at most one hit on the other side of a join.
So, the big question is around whether you can make a FK against the CIX of an Indexed View. And the answer is no.
create table dbo.testtable (id int identity(1,1) primary key, val int not null);
go
create view dbo.testview with schemabinding as
select id, val
from dbo.testtable
where val >= 50
;
go
insert dbo.testtable
select 20 union all
select 30 union all
select 40 union all
select 50 union all
select 60 union all
select 70
go
create unique clustered index ixV on dbo.testview(id);
go
create table dbo.secondtable (id int references dbo.testview(id));
go
All this works except for the last statement, which errors with:
Msg 1768, Level 16, State 0, Line 1
Foreign key 'FK__secondtable__id__6A325CF7' references object 'dbo.testview' which is not a user table.
So the Foreign key must reference a user table.
But... the next question is about whether you could reference a unique index that is filtered in SQL 2008, to achieve a view-like FK.
And still the answer is no.
create unique index ixUV on dbo.testtable(val) where val >= 50;
go
This succeeded.
But now if I try to create a table that references the val column
create table dbo.thirdtable (id int identity(1,1) primary key, val int not null check (val >= 50) references dbo.testtable(val));
(I was hoping that the check constraint that matched the filter in the filtered index might help the system understand that the FK should hold)
But I get an error saying:
There are no primary or candidate keys in the referenced table 'dbo.testtable' that matching the referencing column list in the foreign key 'FK__thirdtable__val__0EA330E9'.
If I drop the filtered index and create a non-filtered unique non-clustered index, then I can create dbo.thirdtable without any problems.
So I'm afraid the answer still seems to be No.
It took me some time to figure out the misunderstaning here -- not sure if I still understand completely, but here it is.
I will use an example, close to yours, but with some data -- easier for me to think in these terms.
So first two tables; A = Department B = Employee
CREATE TABLE Department
(
DepartmentID int PRIMARY KEY
,DepartmentName varchar(20)
,DepartmentColor varchar(10)
)
GO
CREATE TABLE Employee
(
EmployeeID int PRIMARY KEY
,EmployeeName varchar(20)
,DepartmentID int FOREIGN KEY REFERENCES Department ( DepartmentID )
)
GO
Now I'll toss some data in
INSERT INTO Department
( DepartmentID, DepartmentName, DepartmentColor )
SELECT 1, 'Accounting', 'RED' UNION
SELECT 2, 'Engineering', 'BLUE' UNION
SELECT 3, 'Sales', 'YELLOW' UNION
SELECT 4, 'Marketing', 'GREEN' ;
INSERT INTO Employee
( EmployeeID, EmployeeName, DepartmentID )
SELECT 1, 'Lyne', 1 UNION
SELECT 2, 'Damir', 2 UNION
SELECT 3, 'Sandy', 2 UNION
SELECT 4, 'Steve', 3 UNION
SELECT 5, 'Brian', 3 UNION
SELECT 6, 'Susan', 3 UNION
SELECT 7, 'Joe', 4 ;
So, now I'll create a view on the first table to filter some departments out.
CREATE VIEW dbo.BlueDepartments
AS
SELECT * FROM dbo.Department
WHERE DepartmentColor = 'BLUE'
GO
This returns
DepartmentID DepartmentName DepartmentColor
------------ -------------------- ---------------
2 Engineering BLUE
And per your example, I'll add a view for the second table which does not filter anything.
CREATE VIEW dbo.AllEmployees
AS
SELECT * FROM dbo.Employee
GO
This returns
EmployeeID EmployeeName DepartmentID
----------- -------------------- ------------
1 Lyne 1
2 Damir 2
3 Sandy 2
4 Steve 3
5 Brian 3
6 Susan 3
7 Joe 4
It seems to me that you think that Employee No 5, DepartmentID = 3 points to nowhere?
"You'll end up with entries in the
second view that point nowhere."
Well, it points to the Department table DepartmentID = 3, as specified with the foreign key. Even if you try to join view on view nothing is broken:
SELECT e.EmployeeID
,e.EmployeeName
,d.DepartmentID
,d.DepartmentName
,d.DepartmentColor
FROM dbo.AllEmployees AS e
JOIN dbo.BlueDepartments AS d ON d.DepartmentID = e.DepartmentID
ORDER BY e.EmployeeID
Returns
EmployeeID EmployeeName DepartmentID DepartmentName DepartmentColor
----------- -------------------- ------------ -------------------- ---------------
2 Damir 2 Engineering BLUE
3 Sandy 2 Engineering BLUE
So nothing is broken here, the join simply did not find matching records for DepartmentID <> 2 This is actually the same as if I join tables and then include filter as in the first view:
SELECT e.EmployeeID
,e.EmployeeName
,d.DepartmentID
,d.DepartmentName
,d.DepartmentColor
FROM dbo.Employee AS e
JOIN dbo.Department AS d ON d.DepartmentID = e.DepartmentID
WHERE d.DepartmentColor = 'BLUE'
ORDER BY e.EmployeeID
Returns again:
EmployeeID EmployeeName DepartmentID DepartmentName DepartmentColor
----------- -------------------- ------------ -------------------- ---------------
2 Damir 2 Engineering BLUE
3 Sandy 2 Engineering BLUE
In both cases joins do not fail, they simply do as expected.
Now I will try to break the referential integrity through a view (there is no DepartmentID= 127)
INSERT INTO dbo.AllEmployees
( EmployeeID, EmployeeName, DepartmentID )
VALUES( 10, 'Bob', 127 )
And this results in:
Msg 547, Level 16, State 0, Line 1
The INSERT statement conflicted with the FOREIGN KEY constraint "FK__Employee__Depart__0519C6AF". The conflict occurred in database "Tinker_2", table "dbo.Department", column 'DepartmentID'.
If I try to delete a department through the view
DELETE FROM dbo.BlueDepartments
WHERE DepartmentID = 2
Which results in:
Msg 547, Level 16, State 0, Line 1
The DELETE statement conflicted with the REFERENCE constraint "FK__Employee__Depart__0519C6AF". The conflict occurred in database "Tinker_2", table "dbo.Employee", column 'DepartmentID'.
So constraints on underlying tables still apply.
Hope this helps, but then maybe I misunderstood your problem.
Peter already hit on this, but the best solution is to:
Create the "main" logic (that filtering the referenced table) once.
Have all views on related tables join to the view created for (1), not the original table.
I.e.,
CREATE VIEW v1 AS SELECT * FROM table1 WHERE blah
CREATE VIEW v2 AS SELECT * FROM table2 WHERE EXISTS
(SELECT NULL FROM v1 WHERE v1.id = table2.FKtoTable1)
Sure, syntactic sugar for propagating filters for views on one table to views on subordinate tables would be handy, but alas, it's not part of the SQL standard. That said, this solution is still good enough -- efficient, straightforward, maintainable, and guarantees the desired state for the consuming code.
If you try to insert, update or delete data through a view, the underlying table constraints still apply.
Something like this in View2 is probably your best bet:
CREATE VIEW View2
AS
SELECT
T2.col1,
T2.col2,
...
FROM
Table2 T2
INNER JOIN Table1 T1 ON
T1.pk = T2.t1_fk
If rolling over tables so that Identity columns will not clash, one possibility would be to use a lookup table that referenced the different data tables by Identity and a table reference.
Foreign keys on this table would work down the line for referencing tables.
This would be expensive in a number of ways
Referential integrity on the lookup table would have to be be enforced using triggers.
Additional storage of the lookup table and indexing in addition to the data tables.
Data reading would almost certainly involve a Stored Procedure or three to execute a filtered UNION.
Query plan evaluation would also have a development cost.
The list goes on but it might work on some scenarios.
Using Rob Farley's schema:
CREATE TABLE dbo.testtable(
id int IDENTITY(1,1) PRIMARY KEY,
val int NOT NULL);
go
INSERT dbo.testtable(val)
VALUES(20),(30),(40),(50),(60),(70);
go
CREATE TABLE dbo.secondtable(
id int NOT NULL,
CONSTRAINT FK_SecondTable FOREIGN KEY(id) REFERENCES dbo.TestTable(id));
go
CREATE TABLE z(n tinyint PRIMARY KEY);
INSERT z(n)
VALUES(0),(1);
go
CREATE VIEW dbo.SecondTableCheck WITH SCHEMABINDING AS
SELECT 1 n
FROM dbo.TestTable AS t JOIN dbo.SecondTable AS s ON t.Id = s.Id
CROSS JOIN dbo.z
WHERE t.Val < 50;
go
CREATE UNIQUE CLUSTERED INDEX NoSmallIds ON dbo.SecondTableCheck(n);
go
I had to create a tiny helper table (dbo.z) in order to make this work, because indexed views cannot have self joins, outer joins, subqueries, or derived tables (and TVCs count as derived tables).
Another approach, depending on your requirements, would be to use a stored procedure to return two recordsets. You pass it filtering criteria and it uses the filtering criteria to query table 1, and then those results can be used to filter the query to table 2 so that it's results are also consistent. Then you return both results.
You could stage the filtered table 1 data to another table. The contents of this staging table are your view 1, and then you build view 2 via a join of the staging table and table 2. This way the proccessing for filtering table 1 is done once and reused for both views.
Really what it boils down to is that view 2 has no idea what kind of filtering you performed in view 1, unless you tell view 2 the filtering criteria, or make it somehow dependent on the results of view 1, which means emulating the same filtering that occurs on view1.
Constraints don't perform any kind of filtering, they only prevent invalid data, or cascade key changes and deletes.
No, you can't create foreign keys on views.
Even if you could, where would that leave you? You would still have to declare the FK after creating the view. Who would declare the FK, you or the user? If the user is sophisticated enough to declare a FK, why couldn't he add an inner join to the referenced view? eg:
create view1 as select a, b, c, d from table1 where a in (1, 2, 3)
go
create view2 as select a, m, n, o from table2 where a in (select a from view1)
go
vs:
create view1 as select a, b, c, d from table1 where a in (1, 2, 3)
go
create view2 as select a, m, n, o from table2
--# pseudo-syntax for fk:
alter view2 add foreign key (a) references view1 (a)
go
I don't see how the foreign key would simplify your job.
Alternatively:
Copy the subset of data into another schema or database. Same tables, same keys, less data, faster analysis, less contention.
If you need a subset of all the tables, use another database. If you only need a subset of some tables, use a schema in the same database. That way your new tables can still reference the non-copied tables.
Then use the existing views to copy the data over. Any FK violations will raise an error and identify which views require editing. Create a job and schedule it daily, if necessary.
From a purely data integrity perspective (and nothing to do with the Query Optimizer), I had considered an Indexed View. I figured you could make a unique index on it, which could be broken when you try to have broken integrity in your underlying tables.
But... I don't think you can get around the restrictions of indexed views well enough.
For example:
You can't use outer joins, or sub-queries. That makes it very hard to find the rows that don't exist in the view. If you use aggregates, you can't use HAVING, so that cuts out some options you could use there too. You can't even have constants in an indexed view if you have grouping (whether or not you use a GROUP BY clause), so you can't even try putting an index on a constant field so that a second row will fall over. You can't use UNION ALL, so the idea of having a count which will break a unique index when it hits a second zero won't work.
I feel like there should be an answer, but I'm afraid you're going to have to take a good look at your actual design and work out what you really need. Perhaps triggers (and good indexes) on the tables involved, so that any changes that might break something can roll it all that.
But I was really hoping to be able to suggest something that the Query Optimizer might be able to leverage to help the performance of your system, but I don't think I can.