how to perform multiple aggregations on a single SQL query - sql

Question

I have a table with Three columns:
GEOID, ParcelID, and PurchaseDate.
The PKs are GEOID and ParcelID which is formatted as such:
GEOID PARCELID PURCHASEDATE
12345 AB123 1/2/1932
12345 sfw123 2/5/2012
12345 fdf323 4/2/2015
12346 dfefej 2/31/2022 <-New GEOID
What I need is an aggregation based on GEOID.
I need to count the number of ParcelIDs from last month PER GEOID
and I need to provide a percentage of that GEOID of all total sold last month.
I need to produce three columns:
GEOID Nbr_Parcels_Sold Percent_of_total
For each GEOID, I need to know how many Parcels Sold Last month, and with that Number, find out how much percentage that entails for all Solds.
For example: if there was 20 Parcels Sold last month, and 4 of them were sold from GEOID 12345, then the output would be:
GEOID Nbr_Parcels_Sold Perc_Total
12345 4 .2 (or 20%)
I am having issues with the dual aggregation. The concern is that the table in question has over 8 million records.
if there is a SQL Warrior out here who have seen this issue before, Any wisdom would be greatly appreciated.
Thanks.

Answer 1

Hopefully you are using SQL Server 2005 or later version, in which case you can get advantage of windowed aggregation. In this case, windowed aggregation will allow you to get the total sale count alongside counts per GEOID and use the total in calculations. Basically, the following query returns just the counts:
SELECT
GEOID,
Nbr_Parcels_Sold = COUNT(*),
Total_Parcels_Sold = SUM(COUNT(*)) OVER ()
FROM
dbo.atable
GROUP BY
GEOID
;
The COUNT(*) call gives you counts per GEOID, according to the GROUP BY clause. Now, the SUM(...) OVER expression gives you the grand total count in the same row as the detail count. It is the empty OVER clause that tells the SUM function to add up the results of COUNT(*) across the entire result set. You can use that result in calculations just like the result of any other function (or any expression in general).
The above query simply returns the total value. As you actually want not the value itself but a percentage from it for each GEOID, you can just put the SUM(...) OVER call into an expression:
SELECT
GEOID,
Nbr_Parcels_Sold = COUNT(*),
Percent_of_total = COUNT(*) * 100 / SUM(COUNT(*)) OVER ()
FROM
dbo.atable
GROUP BY
GEOID
;
The above will give you integer percentages (truncated). If you want more precision or a different representation, remember to cast either the divisor or the dividend (optionally both) to a non-integer numeric type, since SQL Server always performs integral division when both operands are integers.

Answer 2

How about using sub-query to count the sum
WITH data AS
(
SELECT *
FROM [Table]
WHERE
YEAR(PURCHASEDATE) * 100 + MONTH(PURCHASEDATE) = 201505
)
SELECT
GEOID,
COUNT(*) AS Nbr_Parcels_Sold,
CONVERT(decimal(18,8), COUNT(*)) /
(SELECT COUNT(*) FROM data) AS Perc_Total
FROM
data t
GROUP BY
GEOID
EDIT
To update another table by the result, use UPDATE under WITH()
WITH data AS
(
SELECT *
FROM [Table]
WHERE
YEAR(PURCHASEDATE) * 100 + MONTH(PURCHASEDATE) = 201505
)
UPDATE target SET
Nbr_Parcels_Sold = source.Nbr_Parcels_Sold,
Perc_Total = source.Perc_Total
FROM
[AnotherTable] target
INNER JOIN
(
SELECT
GEOID,
COUNT(*) AS Nbr_Parcels_Sold,
CONVERT(decimal(18,8), COUNT(*)) /
(SELECT COUNT(*) FROM data) AS Perc_Total
FROM
data t
GROUP BY
GEOID
) source ON target.GEOID = source.GEOID

Answer 3

Try the following. It grabs the total sales into a variable then uses it in the subsequent query:
DECLARE #pMonthStartDate DATETIME
DECLARE #MonthEndDate DATETIME
DECLARE #TotalPurchaseCount INT
SET #pMonthStartDate = <EnterFirstDayOfAMonth>
SET #MonthEndDate = DATEADD(MONTH, 1, #pMonthStartDate)
SELECT
#TotalPurchaseCount = COUNT(*)
FROM
GEOIDs
WHERE
PurchaseDate BETWEEN #pMonthStartDate
AND #MonthEndDate
SELECT
GEOID,
COUNT(PARCELID) AS Nbr_Parcels_Sold,
CAST(COUNT(PARCELID) AS FLOAT) / CAST(#TotalPurchaseCount AS FLOAT) * 100.0 AS Perc_Total
FROM
GEOIDs
WHERE
ModifiedDate BETWEEN #pMonthStartDate
AND #MonthEndDate
GROUP BY
GEOID
I'm guessing your table name is GEOIDs. Change the value of #pMonthStartDate to suit yourself. If your PKs are as you say then this will be a quick query.