How do I dynamically generate dates between two dates in Snowflake? - snowflake-cloud-data-platform

Question

I've been searching for a good generate_series analog in Snowflake but what I've found so far is a bit limiting in scope. Most of the examples I've seen use rowcount but I need something more dynamic than that.
I have these columns:
location_id, subscription_id, start_date, end_date
The datediff of the date columns is usually a year but there are many instances where it isn't so I need to account for that.
How do I generate a gapless date range between my start and end dates?
Thank you!

Answer 1

There are several ways to approach this, but here's the way I do it with SQL Generator function Datespine_Groups.
The reason I like to do it this way, is because its flexible enough that I can add weekly, hourly, or monthly intervals between the dates and reuse the code.
The parameter group bounds changes the way the join happens in a subtle way that allows you to control how the dates get filtered out:
global - every location_id, subscription_id combination will start on the same start_date
local - every location_id, subscription_id has their own start/end dates based on the first and last values in the date column
mixed - every location_id, subscription_id has their own start/end dates, but they all share the same end date
Rather than try and make it perfect in 1 query, I think it's probably easier to generate it with mixed and then filter out where the group_start_date occurs after the end_date of your original data.
Here's the SQL. At the very beginning you can either (1) find a way to dynamically generate the 3 parameters, or (2) hard code a ridiculous range that'll last your career and let the rest of the query filter them out :)
You can change month to another datepart, I only assumed you were looking for monthly.
WITH GLOBAL_SPINE AS (
SELECT
ROW_NUMBER() OVER (
ORDER BY
NULL
) as INTERVAL_ID,
DATEADD(
'month',
(INTERVAL_ID - 1),
'2018-01-01T00:00' :: timestamp_ntz
) as SPINE_START,
DATEADD(
'month', INTERVAL_ID, '2018-01-01T00:00' :: timestamp_ntz
) as SPINE_END
FROM
TABLE (
GENERATOR(ROWCOUNT => 2192)
)
),
GROUPS AS (
SELECT
location_id,
subscription_id,
MIN(start_date) AS LOCAL_START,
MAX(start_date) AS LOCAL_END
FROM
My_First_Table
GROUP BY
location_id,
subscription_id
),
GROUP_SPINE AS (
SELECT
location_id,
subscription_id,
SPINE_START AS GROUP_START,
SPINE_END AS GROUP_END
FROM
GROUPS G CROSS
JOIN LATERAL (
SELECT
SPINE_START,
SPINE_END
FROM
GLOBAL_SPINE S
WHERE
S.SPINE_START >= G.LOCAL_START
)
)
SELECT
G.location_id AS GROUP_BY_location_id,
G.subscription_id AS GROUP_BY_subscription_id,
GROUP_START,
GROUP_END,
T.*
FROM
GROUP_SPINE G
LEFT JOIN My_First_Table T ON start_date >= G.GROUP_START
AND start_date < G.GROUP_END
AND G.location_id = T.location_id
AND G.subscription_id = T.subscription_id