SQL Server : getting sum of values in "calendar" table without joining - sql

Question

Is it possible to get a the sum of value from the calendar_table to the main_table without joining like below?
select
date, sum(value)
from
main_table
inner join
calendar_table on start_date <= date and end_date >= date
group by
date
I am trying to avoid a join like this because main_table is a very large table with rows that have very large start and end dates, and it is absolutely killing my performance. And I've already indexed both tables.
Sample desired results:
+-----------+-------+
| date | total |
+-----------+-------+
| 7-24-2010 | 11 |
+-----------+-------+
Sample tables
calendar_table:
+-----------+-------+
| date | value |
+-----------+-------+
| 7-24-2010 | 5 |
| 7-25-2010 | 6 |
| ... | ... |
| 7-23-2020 | 2 |
| 7-24-2020 | 10 |
+-----------+-------+
main_table:
+------------+-----------+
| start_date | end_date |
+------------+-----------+
| 7-24-2010 | 7-25-2010 |
| 8-1-2011 | 8-5-2011 |
+------------+-----------+

Answer 1

You want the sum in the calendar table. So, I would recommend an "incremental" approach. This starts by unpivoting the data and putting the value as an increment and decrement in the results:
select c.date, c.value as inc
from main_table m join
calendar_table t
on m.start_date = c.date
union all
select dateadd(day, 1, c.date), - c.value as inc
from main_table m join
calendar_table t
on m.end_date = c.date;
The final step is to aggregate and do a cumulative sum:
select date, sum(inc) as value_on_date,
sum(sum(inc)) over (order by date) as net_value
from ((select c.date, c.value as inc
from main_table m join
calendar_table t
on m.start_date = c.date
) union all
(select dateadd(day, 1, c.date), - c.value as inc
from main_table m join
calendar_table t
on m.end_date = c.date
)
) c
group by date
order by date;
This is processing two rows of data for each row in the master table. Assuming that your time spans are longer than two days typically for each master row, the resulting data processed should be much smaller. And smaller data implies a faster query.

Answer 2

Here's a cross-apply example to possibly work from.
select main_table.date
, CalendarTable.ValueSum
from main_table
CROSS APPLY(
SELECT SUM(value) as ValueSum
FROM calendar_table
WHERE start_date <= main_table.date and main_table.end_date >= date
) as CalendarTable
group by date

Answer 3

You could try something like this ... but be aware, it is still technically 'joined' to the main table. If you look at an execution plan, you will see that there is a join operation of some kind going on.
select
date,
(select sum(value) from calendar_table t where m.start_date <= t.date and m.end_date >= t.date)
from
main_table m
The thing about that query is that the 'main_table' is not grouped as part of the results. You could possibly do that outside the select, but I don't know what you are trying to achieve. If you are grouping just to get the SUM, then perhaps maintaining the 'main_table' in the group is superflous.

Answer 4

As already mentioned, you must perform a join of some sort in order to get data from more than one table in a query.
You did not provide details if the indexes which are important for performance. I suggest the following indexes to optimize query performance.
For calendar_table, make sure you have a unique clustered index (or primary key) on date. Alternatively, a unique nonclustered index on date with the value column included.
A composite index on the main_table start_date and end_date columns may also be beneficial.
Even with optimal indexes, the query will still take some time against a 500M row table (e.g. a couple of minutes) with no additional filter criteria. If you need results in milliseconds, create an indexed view to materialize the join and aggregation results. Be aware the indexed view will add overhead for inserts/deletes on both tables as well as for updates to the value column in order to keep the index consistent with the underlying data.
Below is an indexed view DDL example.
CREATE VIEW dbo.vw_example
WITH SCHEMABINDING
AS
SELECT
date, sum(value) AS value, COUNT_BIG(*) AS countbig
from
dbo.main_table
inner join
dbo.calendar_table on start_date <= date and end_date >= date
group by
date;
GO
CREATE UNIQUE CLUSTERED INDEX cdx ON dbo.vw_example(date);
GO
Depending on your SQL Server edition, the optimizer may be able to use the indexed view automatically so your original query can use the view index without changes. Otherwise, query the view directly and specify a NOEXPAND hint:
SELECT date, value AS total
FROM dbo.vw_example WITH (NOEXPAND);
EDIT:
With the query improvement #GordonLinoff suggested, a non-clustered index on the main_table end_date column will help optimize that query.