SQL Aggregate Function Query not Producing Expected Results - sql

Question

The following is my query to go through about a million rows to calculate MTBUR (Mean Time Before Unscheduled Repair):
DECLARE #BeginDate date = '01-01-2013',
#EndDate date = '12-31-2013'
BEGIN
SELECT H.AutoType,
COALESCE(((SUM(H.Hours))/(CASE WHEN R.ReceivedDate BETWEEN #BeginDate AND #EndDate THEN COUNT(R.Confirmed) END)), SUM(H.Hours)) AS 'MTBUR'
FROM Hours H
INNER JOIN Repair R
ON H.SN = R.SN
WHERE (R.Confirmed NOT LIKE 'C%' AND R.Confirmed NOT LIKE 'O%')
AND (H.Date BETWEEN #BeginDate AND #EndDate)
GROUP BY H.AutoType,
R.ReceivedDate
END
The following are example results for 2 types:
Type | MTBUR
------------
a | value
a | value
a | value
b | value
b | value
b | value
I want my results to look like this:
Type | MTBUR
------------
a | value
b | value
Why is it grouping the same type several times. I want only 1 value for each type.
Also, Why is the DBMS making me also group by ReceivedDate? I get the feeling that is screwing my results up. Any suggestions?
The following are my CREATE TABLE:
CREATE TABLE [dbo].[acss_hours](
[hoursId] [uniqueidentifier] NOT NULL,
[name] [nvarchar](100) NULL,
[Type] [nvarchar](100) NULL,
[SN] [nvarchar](100) NULL,
[Reg] [nvarchar](100) NULL,
[Hours] [float] NULL,
[Date] [datetime] NULL)
CREATE TABLE [dbo].[repair](
[repairId] [uniqueidentifier] NOT NULL,
[Part] [nvarchar](100) NULL,
[Customer] [nvarchar](100) NULL,
[AutoType] [nvarchar](100) NULL,
[ReceivedDate] [datetime] NULL,
[Confirmed] [nvarchar](100) NULL,
[Company] [nvarchar](100) NULL,
[Reg] [nvarchar](100) NULL,
[Manu] [nvarchar](100) NULL,
[SN] [nvarchar](100) NULL)

Answer 1

You are correct, adding ReceivedDate is screwing up your results. You are getting one row for each type for RecievedDate.
SQL Server if forcing you to add RecievedDate to the group by because you are using it in the select clause. When SQL Server processes each AutoType, what ReceivedDate should it use? It has multiple ReceivedDates per AutoType. Either it needs to use each seperate ReceivedDate by adding it to the group by, or it can use a aggregate function like min or max to select one of the RecievedDates.
How do you want your query to handle it?
I think you should wrap your case in the COUNT.
COUNT(CASE WHEN R.ReceivedDate BETWEEN #BeginDate AND #EndDate
THEN R.Confirmed ELSE 0 END)

Answer 2

You need to include R.ReceivedDate from your calculation in the group by because you're evaluating the column with the between statement. Its the same as including the column in the select. Basically any column in the select line that doesn't have an aggregation function needs to be in the group by.

Answer 3

You will have to make use of the keyword DISTINCT.
So effectively, you can query as such:
DECLARE #BeginDate date = '01-01-2013',
#EndDate date = '12-31-2013'
BEGIN
SELECT DISTINCT H.AutoType,
COALESCE(((SUM(H.Hours))/(CASE WHEN R.ReceivedDate BETWEEN #BeginDate AND #EndDate THEN COUNT(R.Confirmed) END)), SUM(H.Hours)) AS 'MTBUR'
FROM Hours H
INNER JOIN Repair R ON H.SN = R.SN
WHERE (R.Confirmed NOT LIKE 'C%' AND R.Confirmed NOT LIKE 'O%')
AND (H.Date BETWEEN #BeginDate AND #EndDate)
GROUP BY H.AutoType, R.ReceivedDate
END
Hope this helps!!!

Answer 4

Didn't let me post this in the comment. Try an inner query:
SELECT H.AutoType, COALESCE(((SUM(H.Hours))/(SUM(x.CountConfirmed))), SUM(H.Hours)) AS 'MTBUR'
FROM
(SELECT H.AutoType, CASE WHEN R.ReceivedDate BETWEEN #BeginDate AND #EndDate THEN 1 ELSE 0 END AS CountConfirmed
FROM Hours H
INNER JOIN Repair R
ON H.SN = R.SN
WHERE (R.Confirmed NOT LIKE 'C%' AND R.Confirmed NOT LIKE 'O%')
AND (H.Date BETWEEN #BeginDate AND #EndDate)) x
JOIN Hours H
ON H.AutoType = x.AutoType
WHERE (H.Date BETWEEN #BeginDate AND #EndDate)
GROUP BY H.AutoType