Extracting null fields in SQL Server - sql

Question

I will try to be as detailed as possible. Our corporate controller has asked me for some information regarding our suppliers. Here are the tables:
spp = supplier table, each supplier has one record, there are 5,222 records
ast = supplier account profile, there is a (M, 1) relationship between this table and spp, there are 8,950 records in this table. Each duplicate spp_id has a different atp_id which is a transaction profile.
crt = bank account information, a supplier may or may not have bank account info
xvd = table of checking tables, xvd.xcd_id is the field that holds the checking table id. Checking table 0007 is the table that contains the discount info.
Here is my script:
select spp.spp_id supp_num,
spp.spp_matchname supp_name,
case when spp.spp_ddcalculation = 0
then 'End of Month'
else
case when spp.spp_ddcalculation = 1
then 'Net'
else
case when spp.spp_ddcalculation = 2
then 'End of 10, 20, 30'
else
case when spp.spp_ddcalculation = 3
then 'End of 15 or 30'
else null
end
end
end
end calculation1,
convert(varchar(2), spp.spp_ddduration) + case when spp.spp_ddmd = 0
then ' Days'
else case when spp.spp_ddmd = 1
then ' Months'
else null
end
end duration1,
spp.spp_ddday stop_day1,
xvd.xvd_desc discount,
crt.crt_name bank,
case when ast.ast_ddcalculation = 0
then 'End of Month'
else
case when ast.ast_ddcalculation = 1
then 'Net'
else
case when ast.ast_ddcalculation = 2
then 'End of 10, 20, 30'
else case when ast.ast_ddcalculation = 3
then 'End of 15 or 30'
else null
end
end
end
end
calculation2,
convert(varchar(2), ast.ast_ddduration) + case when ast.ast_ddmd = 0
then ' Days'
else case when ast.ast_ddmd = 1
then ' Months'
else null
end
end
duration2,
ast.ast_ddday stop_day2
from spp left join ast on spp.spp_id = ast.spp_id
left join crt on ast.crt_id = crt.crt_id
inner join xvd on ast.cfd_id = xvd.xcv_id
where xvd.xcd_id = '0007'
and xvd.lng_id = 0
order by spp.spp_id
The problem is that there are 371 records in the ast table that have a non null cfd_id which is the field that relates to the discount in checking table 0007. When I run this I get 371 records, but I need all suppliers, even those with null discounts. I know the problem is a combination of my joins and the fact that there is not a null xcv_id in checking table 0007. Can anyone see anything glaring that I have overlooked?
To recap, there are 8,950 records in ast, but only 371 of them have a non null cfd_id. I need to grab all 8,950 records, I can't seem to extract the null discounts. I think I can probably pull everything into a temp table then grab the discounts, but am wondering if there is a way to do this in one select statement.
Thanks
Tony
Edit: The last line of my from statement seems to be the primary issue
inner join xvd on ast.cfd_id = xvd.xcv_id
There are no null xcv_id but there are null cfd_id. Is there another way to join those two tables, besides checking for equality?
Forgot to mention, we are on SQL Server 2008 R2.

Answer 1

Does this solve the problem ?
FROM spp
LEFT JOIN ast
ON spp.spp_id = ast.spp_id
LEFT JOIN crt
ON ast.crt_id = crt.crt_id
INNER JOIN xvd
ON xvd.xcv_id = ast.cfd_id
WHERE xvd.xcd_id = '0007'
AND xvd.lng_id = 0

Answer 2

I think you can just change your inner join to a left join:
from spp left join ast on spp.spp_id = ast.spp_id
left join crt on ast.crt_id = crt.crt_id
inner join xvd on ast.cfd_id = xvd.xcv_id
to
from spp left join ast on spp.spp_id = ast.spp_id
left join crt on ast.crt_id = crt.crt_id
left join xvd on ast.cfd_id = xvd.xcv_id
If you are saying that you want to select records where xvd.xcd_id is 0007 or null then change your where clause to this:
(xvd.xcd_id = '0007' OR xvd.xcd_id is null)

Answer 3

This sounds like a perfect use for views. Instead of trying to build one complex query, you could build a series of views that build upon one another filtering the data the way you want it... then apply the final query to the last view.