Multi-row action for Instead of trigger SQL Server - sql-server-2008

Question

Scenario/background:
I am trying to create a table of "Tests". For purposes of this question my table will only have 5 columns defined as follows:
CREATE TABLE TestTable
(
Id UNIQUEIDENTIFIER DEFAULT NEWID() NOT NULL,
Name VARCHAR(75) NOT NULL,
DateRequested DATETIME NOT NULL DEFAULT GETDATE(),
TestYear AS YEAR(DateRequested) PERSISTED NOT NULL, -- computed column that shows the year the test was requested. I want to persist this column so I can index on it if need be.
TestNumber CHAR(4) NOT NULL DEFAULT '0000', -- need this to auto increment but also needs to reset for the first test of the year.
CONSTRAINT TestTablePK PRIMARY KEY(Id)
);
GO
My requirement is that I want the 'TestNumber' to "auto-increment" based on the year. For example:
GUID, Test 1 in Old Yr, 2013-01-01 05:00:00.000, 2013, 0001
GUID, Test 2 in Old Yr, 2013-12-25 11:00:00.000, 2013, 0002
GUID, Test 3 in Old Yr, 2013-12-26 09:00:00.000, 2013, 0003
...., ................, ......................., ...., N
GUID, Test N in Old Yr, 2013-12-31 09:00:00.000, 2013, N+1
GUID, Test 1 in New Yr, 2014-01-01 11:00:00.000, 2014, 0001 <-- reset to 1
I was thinking that it would be an auto-increment column but how would I reset it based on this being the first test of a new year? So my incorrect solution thus far has been an "instead of insert" trigger defined as follows:
CREATE TRIGGER InsteadOfInsertTrigger ON dbo.TestTable
INSTEAD OF INSERT AS
BEGIN
-- Get the year of the test request being inserted from the pseudo-insert table.
DECLARE #TestYear INT;
SET #TestYear = (SELECT YEAR(DateRequested) FROM inserted);
-- Grab the maximum TestNumber from TestTable based on the year
-- that we are inserting a record for.
DECLARE #MaxTestNumber INT;
SET #MaxTestNumber = (SELECT MAX(TestNumber) FROM dbo.TestTable WHERE TestYear = #TestYear);
-- If this is the first test of the year being inserted it is a special case
IF #MaxTestNumber IS NULL
BEGIN
SET #MaxTestNumber = 0;
END;
-- Here we take the MaxTestNumber, add 1 to it, and then pad it with
-- the appropriate number of zero's in front of it
DECLARE #TestNumber VARCHAR(4);
SET #TestNumber = (SELECT RIGHT('0000' + CAST((#MaxTestNumber + 1) AS VARCHAR(4)), 4));
INSERT INTO dbo.TestTable(Name, DateRequested, TestNumber)
SELECT Name, DateRequested, #TestNumber FROM inserted;
END;
GO
Now here is some DML showing the trigger in action:
INSERT INTO TestTable(Name, DateRequested)
VALUES('Some Test', '05-05-2013');
INSERT INTO TestTable(Name, DateRequested)
VALUES('Some Other Test', '12-25-2013');
INSERT INTO TestTable(Name, DateRequested)
VALUES('Blah Blah', '12-31-2013');
INSERT INTO TestTable(Name, DateRequested)
VALUES('Foo', '01-01-2014');
SELECT * FROM TestTable ORDER BY TestYear ASC, TestNumber ASC;
So as you can see my trigger works for single row inserts but a keen eye will be able to tell it will not work for multi-row inserts.
CREATE TABLE TempTestTable
(
Name VARCHAR(75) NOT NULL,
DateRequested DATETIME NOT NULL DEFAULT GETDATE()
);
GO
INSERT INTO TempTestTable(Name, DateRequested)
VALUES('Test1', '01-01-2012');
INSERT INTO TempTestTable(Name, DateRequested)
VALUES('Test2', '12-25-2012');
INSERT INTO TempTestTable(Name, DateRequested)
VALUES('Test3', '01-01-2013');
INSERT INTO TempTestTable(Name, DateRequested)
VALUES('Test4', '01-01-2014');
-- This doesnt work because it is a multi-row insert.
INSERT INTO TestTable(Name, DateRequested)
SELECT Name, DateRequested FROM TempTestTable;
My Question
I realize that I can probably handle this with stored procedures and force users to use stored procedures when updating the tables but I want to be extra careful and prevent sysadmins from being able to do direct inserts to the table with an incorrect 'TestNumber'.
So StackOverflow, my question is how can I achieve this? Would I use a cursor inside of my InsteadOfInsertTrigger? I am looking for alternatives.

Answer 1

Not the neatest thing I'll ever write, but seems to do the job:
CREATE TRIGGER InsteadOfInsertTrigger ON dbo.TestTable
INSTEAD OF INSERT AS
BEGIN
;With Years as (
select i.TestYear,
COALESCE(MAX(tt.TestNumber),0) as YMax
from inserted i left join TestTable tt
on i.TestYear = tt.TestYear
group by i.TestYear
), Numbered as (
select i.ID,i.Name,i.DateRequested,
RIGHT('000' + CONVERT(varchar(4),
ROW_NUMBER() OVER (PARTITION BY i.TestYear
ORDER BY i.DateRequested,i.Id) + YMax)
,4) as TestNumber
from inserted i
inner join
Years y
on
i.TestYear = y.TestYear
)
insert into TestTable (Id,Name,DateRequested,TestNumber)
select Id,Name,DateRequested,TestNumber from Numbered;
END;
The first CTE (Years) finds the highest used number for each year that's of interest. The second CTE (Numbered) then uses those values to offset a ROW_NUMBER() that's being assessed over all rows in inserted. I picked the ORDER BY columns for the ROW_NUMBER() so that it's as deterministic as possible.
(I was confused about one thing for a while, but it turns out that I can use TestYear from inserted rather than having to repeat the YEAR(DateRequested) formula)