Question

I’ve been reading documentation and looking at FAQs and haven’t found an answer for this one which probably means it can’t be done. My actual situation is a little more complex, but I’ll try to simplify it for this question. For each of the past years, I have a header/detail tables with a foreign key linking them. The year datum is in the header records! I want to be able to query all tables concatenated across years.

I have set up views that follows a ‘SELECT + UNION ALL’ format. I’ve also put check constraints on the header tables to restrict their values to their respective year. This allows the SQL server query optimizer to only query specific tables when running a query that is restricted with a WHERE clause. Awesome. Up to this point, this information can be found anywhere and everywhere by searching for Partitioned Views.

I want to do the same sort of query optimization with the detail tables but can’t figure it out. There is nothing in the detail record that indicates what year it belongs to without joining with the header record; Meaning, the foreign key constraint is the only constraint I have to go off of.

The only solution I’ve thought of is adding a ‘year’ column to the detail tables and then adding another where sub clause to the queries. Is there any thing I can do to create a partitioned view of the detail tables using the existing foreign key constraint?

---

Here is some DDL for reference:

CREATE TABLE header2008 (
    hid INT PRIMARY KEY,
    dt DATE CHECK ('2008-01-01' <= dt AND dt < '2009-01-01')
)

CREATE TABLE header2009 (
    hid INT PRIMARY KEY,
    dt DATE CHECK ('2009-01-01' <= dt AND dt < '2010-01-01')
)

CREATE TABLE detail2008 (
    did INT PRIMARY KEY,
    hid INT FOREIGN KEY REFERENCES header2008(hid),
    value INT
)

CREATE TABLE detail2009 (
    did INT PRIMARY KEY,
    hid INT FOREIGN KEY REFERENCES header2009(hid),
    value INT
)

GO
CREATE VIEW headerAll AS
SELECT * FROM header2008 UNION ALL
SELECT * FROM header2009
GO

CREATE VIEW detailAll AS
SELECT * FROM detail2008 UNION ALL
SELECT * FROM detail2009
GO

--This only hits the header2008 table (GOOD)
SELECT * 
FROM headerAll h
WHERE dt = '2008-04-04'

--This hits the header2008, detail2008, and detail 2009 tables. (BAD)
SELECT * 
FROM headerAll h
INNER JOIN detailAll d ON h.hid = d.hid
WHERE dt = '2008-04-04'

Answer 1

Since you’re not going for partitioned tables, I’m assuming you can’t target 2005+ Enterprise Edition or higher.

Here is an alternative to adding a new physical column to your tables:

CREATE VIEW detailAll AS
    SELECT 2008 AS Year, * FROM detail2008
    UNION ALL
    SELECT 2009, * FROM detail2009

then,

SELECT * 
    FROM headerAll h
    INNER JOIN detailAll d ON h.hid = d.hid
    WHERE dt = '2008-04-04' AND d.Year = 2008

Before you run off and implement this, there is a catch; well, two catches actually.

This solution, like the headerAll view as it’s written, cannot accommodate parameters on the partitioning column and still do partition elimination. Using a search predicate of WHERE dt = @date AND d.Year = YEAR(@date) causes table scans across all tables in both views because the query optimizer assumes @date is an arbitrary value (and there’s no way to fix that). This is a recipe for a performance disaster if the view is exposed publicly in your database API: there is no restriction on parameterization in queries, and most query authors and ORMs tend to use parameterized queries wherever possible (it’s almost always a good thing!).

To get the views to do partition elimination in a real application, you will have to resort to dynamic string execution. How you accomplish this will depend on your business requirements, data requirements, and application architecture. It will be a bit trickier if you’re grabbing data from multiple years.

Note also that using dynamic string execution would allow you to write queries directly against the base tables instead of introducing a UNIONed view for each “table”. I don’t think there’s anything wrong with the latter, but this is an option you may not have considered.