Keeping Specific Dates AND Distinct NULLS - sql

Question

I have the following stored procedure
ALTER PROCEDURE [dbo].[sp_GetFeedDate10_TEST]
-- sp_GetFeedDate10_TEST '05/30/2018'
#daycurrent DATE
AS
BEGIN
SELECT
TANK.Name, TANK.Tank_Pond_uID,
FEED.FeedValue, FEED.Date
FROM
aa_Tanks_Ponds TANK
LEFT JOIN
aa_Feed_Chart FEED ON TANK.Tank_Pond_uID = FEED.Tank_Pond_uID
WHERE
TANK.Site_Name = 'Dry Creek' --and (FEED.Date = DATEADD(DAY, -10, #daycurrent))
ORDER BY
TANK.Tank_Pond_uID
END
I commented out the "and
(FEED.Date = DATEADD(DAY, -10, #daycurrent))
where I am currently having issues with filtering. The join is pulling a list of tanks and joining with any feed values and dates from another list.
Where I run into trouble is when filtering based on the date, I lose all the distinct NULLS for all tanks that don't contain a value. It's important to keep the result the same rows and order as the TANK table.
Here's and example of the first table:
Name Tank_Pond_uID
--------------------
B01 DCB01
B02 DCB02
B03 DCB03
B04 DCB04
B05 DCB05
Example of the second table:
Site_Name Tank_Pond_uID Date FeedValue
--------------------------------------------------
Dry Creek DCB01 2018-05-20 90
Dry Creek DCB02 2018-05-20 90
Dry Creek DCB03 2018-05-20 90
Where I run the above stored procedure with a date:
sp_GetFeedDate10_TEST '05/30/2018'
(I know date doesn't matter as the commented out section needs it), I get the following result:
Name Tank_Pond_uID FeedValue Date
-----------------------------------------------
B01 DCB01 90 2018-05-20
B01 DCB01 90 2018-05-21
B01 DCB01 90 2018-05-22
B02 DCB02 90 2018-05-20
B02 DCB02 90 2018-05-21
B02 DCB02 90 2018-05-22
B03 DCB03 NULL NULL
B04 DCB04 NULL NULL
B05 DCB05 NULL NULL
When I add the commented section back into the Store procedure and run it again I get the following result:
Name Tank_Pond_uID FeedValue Date
-----------------------------------------------
B01 DCB01 90 2018-05-20
B02 DCB02 90 2018-05-20
I would like the expected result to be keep the Left rows and still filter date:
Example of expected table result:
Name Tank_Pond_uID FeedValue Date
-----------------------------------------------
B01 DCB01 90 2018-05-20
B02 DCB02 90 2018-05-20
B03 DCB03 NULL NULL
B04 DCB04 NULL NULL
B05 DCB05 NULL NULL

Answer 1

You have turned your left join into an inner join with the predicates in your where clause. Move the date predicate to the join and this will work.
select TANK.Name
, TANK.Tank_Pond_uID
, FEED.FeedValue,FEED.Date
from aa_Tanks_Ponds TANK
LEFT JOIN aa_Feed_Chart FEED ON TANK.Tank_Pond_uID = FEED.Tank_Pond_uID
and FEED.Date = DATEADD(DAY, -10, #daycurrent)
where TANK.Site_Name = 'Dry Creek'
order by TANK.Tank_Pond_uID