Better way to calculate utilisation - sql

Question

I have a rather complicated (and very inefficient) way of getting utilisation from a large list of periods (Code below).
Currently I'm running this for a period of 8 weeks and it's taking between 30 and 40 seconds to return data.
I need to run this regularly for periods of 6 months, 1 year and two years which will obviously take a massive amount of time.
Is there a smarter way to run this query to lower the number of table scans?
I have tried several ways of joining the data, all seem to return junk data.
I've tried to comment the code as much as I can but if anything is unclear let me know.
Table Sizes:
[Stock] ~12,000 records
[Contitems] ~90,000 records
Pseudocode for clarity:
For each week between Start and End:
Get list of unique items active between dates (~12,000 rows)
For each unique item
Loop through ContItems table (~90,000 rows)
Return matches
Group
Group
Return results
The Code
DECLARE #WEEKSTART DATETIME; -- Used to pass start of period to search
DECLARE #WEEKEND DATETIME; -- Used to pass end of period to search
DECLARE #DC DATETIME; -- Used to increment dates
DECLARE #INT INT; -- days to increment for each iteration (7 = weeks)
DECLARE #TBL TABLE(DT DATETIME, SG VARCHAR(20), SN VARCHAR(50), TT INT, US INT); -- Return table
SET #WEEKSTART = '2012-05-01'; -- Set start of period
SET #WEEKEND = '2012-06-25'; -- Set end of period
SET #DC = #WEEKSTART; -- Start counter at first date
SET #INT = 7; -- Set increment to weeks
WHILE (#DC < #WEEKEND) -- Loop through dates every [#INT] days (weeks)
BEGIN
SET #DC = DATEADD(D,#INT,#DC); -- Add 7 days to the counter
INSERT INTO #TBL (DT, SG, SN, TT, US) -- Insert results from subquery into return table
SELECT #DC, SUB.GRPCODE, SubGrp.NAME, SUM(SUB.TOTSTK), SUM(USED)
FROM
(
SELECT STK.GRPCODE, 1 AS TOTSTK, CASE (SELECT COUNT(*)
FROM ContItems -- Contains list of hires with a start and end date
WHERE STK.ITEMNO = ContItems.ITEMNO -- unique item reference
AND ContItems.DELDATE <= DATEADD(MS,-2,DATEADD(D,#INT,#DC)) -- Hires starting before end of week searching
AND (ContItems.DOCDATE#5 >= #DC -- Hires ending after start of week searching
OR ContItems.DOCDATE#5 = '1899-12-30 00:00:00.000')) -- Or hire is still active
WHEN 0 THEN 0 -- None found return zero
WHEN NULL THEN 0 -- NULL return zero
ELSE 1 END AS USED -- Otherwise return 1
FROM Stock STK - List of unique items
WHERE [UNIQUE] = 1 AND [TYPE] != 4 -- Business rules
AND DATEPURCH < #DC AND (DATESOLD = '1899-12-30 00:00:00.000' OR DATESOLD > DATEADD(MS,-2,DATEADD(D,#INT,#DC))) -- Stock is valid between selected week
) SUB
INNER JOIN SubGrp -- Used to get 'pretty' names
ON SUB.GRPCODE = SubGrp.CODE
GROUP BY SUB.GRPCODE, SubGrp.NAME
END
-- Next section gets data from temp table
SELECT SG, SN, SUM(TT) AS TOT, SUM(US) AS USED, CAST(SUM(US) AS FLOAT) / CAST(SUM(TT) AS FLOAT) AS UTIL
FROM #TBL
GROUP BY SG, SN
ORDER BY TOT DESC

Answer 1

I have two suggestions.
First, rewrite the query to move the "select" statement from the case statement to the from clause:
SELECT #DC, SUB.GRPCODE, SubGrp.NAME, SUM(SUB.TOTSTK), SUM(USED)
FROM (SELECT STK.GRPCODE, 1 AS TOTSTK,
(CASE MAX(Contgrp.cnt) -- Or hire is still active
WHEN 0 THEN 0 -- None found return zero
WHEN NULL THEN 0 -- NULL return zero
ELSE 1
END) AS USED -- Otherwise return 1
FROM Stock STK left outer join -- List of unique items
(SELECT itemno, COUNT(*) as cnt
FROM ContItems -- Contains list of hires with a start and end date
WHERE ContItems.DELDATE <= DATEADD(MS,-2,DATEADD(D,#INT,#DC)) AND -- Hires starting before end of week searching
(ContItems.DOCDATE#5 >= #DC OR -- Hires ending after start of week searching
ContItems.DOCDATE#5 = '1899-12-30 00:00:00.000'
)
group by ITEMNO
) ContGrp
on STK.ITEMNO = ContItems.ITEMNO
WHERE [UNIQUE] = 1 AND [TYPE] != 4 AND -- Business rules
DATEPURCH < #DC AND (DATESOLD = '1899-12-30 00:00:00.000' OR DATESOLD > DATEADD(MS,-2,DATEADD(D,#INT,#DC))) -- Stock is valid between selected week
) SUB INNER JOIN SubGrp -- Used to get 'pretty' names
ON SUB.GRPCODE = SubGrp.CODE
GROUP BY SUB.GRPCODE, SubGrp.NAME
In doing this, I found a something suspicious. The case statement is operating at the level of "ItemNo", but the grouping is by "GrpCode". So, the "Count(*)" is really returning the sum at the group level. Is this what you intend?
The second is to dispense with the WHILE loop, if you have multiple weeks. To do this, you just need to convert DatePurch to an appropriate week. However, if the code usually runs on just one or two weeks, this effort may not help very much.

Answer 2

Well, replacing the DATEADD functions in the WHERE clauses at first.
You already have
SET #DC = DATEADD(D,#INT,#DC);
Why not declare another local variable for deletion date:
WHILE (#DC < #WEEKEND) -- Loop through dates every [#INT] days (weeks)
BEGIN
SET #DC = DATEADD(D,#INT,#DC);
DECLARE #DeletionDate DATETIME = DATEADD(MS,-2,DATEADD(D,#INT,#DC));
And use it in the case statement:
CASE (SELECT COUNT(*) .... AND ContItems.DELDATE <= #DeletionDate ....
And also in the outer where clause...
Then you need to make sure that you have correctly indexed your tables.