Move aggregate logic to separate function in SQL Server 2008 R2 - sql

Question

Please correct me if I'm using the wrong terminology or description, but I have business logic within an aggregate function (MIN and MAX). I wish to move to the logic to it's own function. I wish to do this so I don't have to make multiple changes in different locations when the client requests. I have the following
SELECT DISTINCT
DATA_MONTH,
DATA_DATE,
CASE
WHEN MIN(DATA_YEAR) = MAX(DATA_YEAR)
AND MIN(DATA_YEAR) = #BEGIN_YR THEN 'Started'
WHEN MIN(DATA_YEAR) = MAX(DATA_YEAR)
AND MIN(DATA_YEAR) <> #CURRENTFY THEN
CAST((MIN(DATA_YEAR) %100)-1 AS VARCHAR)
+ '/'
+ CAST(MIN(DATA_YEAR)%100 AS VARCHAR)
WHEN MIN(DATA_YEAR) <> MAX(DATA_YEAR)
AND MIN(DATA_YEAR) = #BEGIN_YR THEN
'Started' + ' from '
+ CAST((MAX(DATA_YEAR) %100)-1 AS VARCHAR)
+ '/'
+ CAST(MAX(DATA_YEAR)%100 AS VARCHAR)
ELSE CAST((MIN(DATA_YEAR) %100)-1 AS VARCHAR)
+ '/'
+ CAST((MIN(DATA_YEAR) %100) AS VARCHAR)
+ ' through '
+ CAST((MAX(DATA_YEAR) %100)-1 AS VARCHAR)
+ '/'
+ CAST(MAX(DATA_YEAR)%100 AS VARCHAR)
END AS [STATUS]
FROM TABLE_A
WHERE DATA_MONTH IN ('03', '04')
AND DATA_DATE = '01'
GROUP BY DATA_MONTH,
DATA_DATE
Which I would like to change it to this:
SELECT DISTINCT
DATA_MONTH,
DATA_DATE,
dbo.getStatus(DATA_YEAR) AS [STATUS]
FROM TABLE_A
WHERE DATA_MONTH IN ('03', '04')
AND DATA_DATE = '01'
GROUP BY DATA_MONTH,
DATA_DATE
The logic for getStatus() has the case statements and can output:
NULL
Started
15/16
Started from 15/16
15/16 through 16/17
My question is how can I restructure my logic to make this possible as I have a GROUP BY clause?

Answer 1

You can create a scalar user defined function and use it in the SELECT. Since it needs to be aggregated, you should be able to throw a MAX around it.
Although, I'd be interested to see if this works.
Nicarus is probably right and that you need a user defined aggregate function.
USE [AdventureWorks2012]
GO
/****** Object: Table [dbo].[TABLE_A] Script Date: 7/20/2016 3:23:39 PM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[TABLE_A](
[DATA_DATE] [date] NULL,
[DATA_MONTH] [int] NOT NULL,
[DATA_YEAR] [int] NOT NULL
) ON [PRIMARY]
GO
INSERT INTO TABLE_A SELECT CAST ('2016-03-02' as DATE) AS DATA_DATE, 3 as DATA_MONTH, 2016 AS DATA_YEAR
CREATE FUNCTION dbo.getStatus(#MAXYR int, #MINYR int, #BEGIN_YR int ,#CURRENTFY int)
RETURNS varchar(30)
AS
BEGIN
DECLARE #ret varchar(30);
SELECT #ret = CASE
WHEN #MINYR = #MAXYR
AND #MINYR = #BEGIN_YR THEN 'Started'
WHEN #MINYR = #MAXYR
AND #MINYR <> #CURRENTFY THEN
CAST((#MINYR %100)-1 AS VARCHAR)
+ '/'
+ CAST(#MINYR%100 AS VARCHAR)
WHEN #MINYR <> #MAXYR
AND #MINYR = #BEGIN_YR THEN
'Started' + ' from '
+ CAST((#MAXYR %100)-1 AS VARCHAR)
+ '/'
+ CAST(#MAXYR%100 AS VARCHAR)
ELSE CAST((#MINYR %100)-1 AS VARCHAR)
+ '/'
+ CAST((#MINYR %100) AS VARCHAR)
+ ' through '
+ CAST((#MAXYR %100)-1 AS VARCHAR)
+ '/'
+ CAST(#MAXYR%100 AS VARCHAR)
END
RETURN #ret;
END;
DECLARE #BEGIN_YR INT = 2;
DECLARE #CURRENTFY int = 2016;
SELECT DISTINCT
DATA_MONTH,
DATA_DATE,
dbo.getStatus(MAX(DATA_YEAR), MIN(DATA_YEAR), #BEGIN_YR, #CURRENTFY) as STATUS
FROM TABLE_A
GROUP BY DATA_MONTH, DATA_DATE