SQL - BigQuery - How do I fill in dates from a calendar table? - sql

Question

My goal is to join a sales program table to a calendar table so that there would be a joined table with the full trailing 52 weeks by day, and then the sales data would be joined to it. The idea would be that there are nulls I could COALESCE after the fact. However, my problem is that I only get results without nulls from my sales data table.
The questions I've consulted so far are:
Join to Calendar Table - 5 Business Days
Joining missing dates from calendar table Which points to
MySQL how to fill missing dates in range?
My Calendar table is all 364 days previous to today (today being day 0). And the sales data has a program field, a store field, and then a start date and an end date for the program.
Here's what I have coded:
SELECT
CAL.DATE,
CAL.DAY,
SALES.ITEM,
SALES.PROGRAM,
SALES.SALE_DT,
SALES.EFF_BGN_DT,
SALES.EFF_END_DT
FROM
CALENDAR_TABLE AS CAL
LEFT JOIN
SALES_TABLE AS SALES
ON CAL.DATE = SALES.SALE_DT
WHERE 1=1
and SALES.ITEM = 1 or SALES.ITEM is null
ORDER BY DATE ASC
What I expected was 365 records with dates where there were nulls and dates where there were filled in records. My query resulted in a few dates with null values but otherwise just the dates where a program exists.
DATE | ITEM | PROGRAM | SALE_DT | PRGM_BGN | PRGM_END |
----------|--------|---------|----------|-----------|-----------|
8/27/2020 | | | | | |
8/26/2020 | | | | | |
8/25/2020 | | | | | |
8/24/2020 | | | | | |
6/7/2020 | 1 | 5 | 6/7/2020 | 2/13/2016 | 6/7/2020 |
6/6/2020 | 1 | 5 | 6/6/2020 | 2/13/2016 | 6/7/2020 |
6/5/2020 | 1 | 5 | 6/5/2020 | 2/13/2016 | 6/7/2020 |
6/4/2020 | 1 | 5 | 6/4/2020 | 2/13/2016 | 6/7/2020 |
Date = Calendar day.
Item = Item number being sold.
Program = Unique numeric ID of program.
Sale_Dt = Field populated if at least one item was sold under this program.
Prgm_bgn = First day when item was eligible to be sold under this program.
Prgm_end = Last day when item was eligible to be sold under this program.
What I would have expected would have been records between June 7 and August 24 which just had the DATE column populated for each day and null values as what happens in the most recent four records.
I'm trying to understand why a calendar table and what I've written are not providing the in-between dates.
EDIT: I've removed the request for feedback to shorten the question as well as an example I don't think added value. But please continue to give feedback as you see necessary.

Answer 1

I'd be more than happy to delete this whole question or have someone else give a better answer, but after staring at the logic in some of the answers in this thread (MySQL how to fill missing dates in range?) long enough, I came up with this:
SELECT
CAL.DATE,
t.* EXCEPT (DATE)
FROM
CALENDER_TABLE AS CAL
LEFT JOIN
(SELECT
CAL.DATE,
CAL.DAY,
SALES.ITEM,
SALES.PROGRAM,
SALES.SALE_DT,
SALES.EFF_BGN_DT,
SALES.EFF_END_DT
FROM
CALENDAR_TABLE AS CAL
LEFT JOIN
SALES_TABLE AS SALES
ON CAL.DATE = SALES.SALE_DT
WHERE 1=1
and SALES.ITEM = 1 or SALES.ITEM is null
ORDER BY DATE ASC) **t**
ON CAL.DATE = t.DATE
From what I can tell, it seems to be what I needed. It allows for the subquery to connect a date to all those records, then just joins on the calendar table again solely on date to allow for those nulls to be created.