MS SQL Server: Load All Data vs Aggregate with +1 round trip - sql

Question

I love to get your opinion on this problem.
I need to show the list of order records for the range of particular date/time. Then summarise it with # of Order compare with the "last" order. "Last" can mean either last month OR last year
Since I am going to show the list of order record, I am thinking to get the record from last month OR last year with one hit (ie. together with the records of current date/time range)
OR, alternatively, I can:
Get the record of current date/time range, THEN
Get the total number of order (using aggregate) for last month OR last year
The alternative means there is 2 round trips to database (but less data to return). Or should I stick with my current method (loading all records including those from last month OR last year).
NOTE: The website and the SQL server is hosted in Microsoft Azure Cloud. But we might switch to AWS in the future.
Thanks
Input example (some fields are omitted including time for simplicity)
----------------------------------------------------------------
| Warehouse Id | Order Id | Product Id | Quantity | Order Date |
----------------------------------------------------------------
| 1 | 10 | 1 | 10 | 2016-09-25 |
| 1 | 9 | 5 | 5 | 2016-09-24 |
| 1 | 8 | 4 | 8 | 2016-09-23 |
| 1 | 7 | 6 | 2 | 2016-09-23 |
| 1 | 6 | 8 | 1 | 2016-09-23 |
| 1 | 5 | 1 | 2 | 2016-09-22 |
| 1 | 4 | 1 | 2 | 2016-09-21 |
| 1 | 3 | 5 | 10 | 2016-09-21 |
| 1 | 2 | 5 | 15 | 2016-08-12 |
| 1 | 1 | 5 | 5 | 2016-08-10 |
----------------------------------------------------------------
The desire OUTPUT:
Input:
WarehouseId: 1
StartDate: 2016-09-01 End Date: 2016-09-30)
Comparison type: Last Month (ie. StartDate: 2016-08-01 EndDate: 2016-08-31)
Output:
Warehouse: xxx
-------------------------------------------------
| Order Id | Product Id | Quantity | Order Date |
-------------------------------------------------
| 10 | 1 | 10 | 2016-09-25 |
| 9 | 5 | 5 | 2016-09-24 |
| 8 | 4 | 8 | 2016-09-23 |
| 7 | 6 | 2 | 2016-09-23 |
| 6 | 8 | 1 | 2016-09-23 |
| 5 | 1 | 2 | 2016-09-22 |
| 4 | 1 | 2 | 2016-09-21 |
| 3 | 5 | 10 | 2016-09-21 |
-------------------------------------------------
Total Order: 40 (increase 100% from last month)
So, what I am doing now is to get ALL records from 2016-08-01 to 2016-09-30. That way I can avoid 2 round trips.
Alternatively, I can do the following:
1. Get record from 2016-09-01 to 2016-09-30
var rec = (from rec in tblOrders
where (rec.WarehouseId == whsId) && (rec.OrderDate >= startDate) && (rec.OrderDate <= endDate)
select rec).ToList();
2. Then do the SUM of total order from 2016-08-01 to 2016-08-31 for comparison purposes
var recSum = (from rec in ef.tblOrders
where (rec.WarehouseId == whsId) && (rec.OrderDate >= cStartDate) && (rec.OrderDate <= cEndDate)
group rec by rec.WarehouseId into grec
select new
{
TotalQty = grec.Sum(x => x.Quantity),
}).FirstOrDefault();

Answer 1

You can do this with window functions:
select o.*
from (select o.*
sum(case when datetime is "last month" or "last year" then 1 else 0 end) over () as last_num_orders
from orders o
) o
where o.datetime between #date1 and #date2;
I am very unclear what "last" means in this context. However, you can do what you want with window functions, which is the preferred option 0.