join with date dimension but don't want NULL for the dates with values - sql

Question

I have a query:
SELECT
d.FiscalMonth,
d.FiscalMonthOfYear,
p.Name
FROM
DimDate d
LEFT JOIN FactSales f on f.SaleDate=d.PKDate
LEFT JOIN DimPerson p on p.PersonId=f.PersonId
WHERE d.FiscalYear='2014/7/1'
group by d.FiscalMonth, d.FiscalMonthOfYear, p.Name
ORDER BY d.FiscalMonthOfYear asc, p.PersonID asc
Which gives me these results:
Which is all fine, I want to include all months, even the ones that don't have data. (In this case FiscalMonth 2-12.)
The problem I have is with that one NULL value where I have data, IE. FiscalMonthOfYear 1. The red box.
How would I go about not returning that one "NULL" for the FiscalMonth=2014-07-01? I've tried some various where clauses but any time I remove the "NULL" values from the results, I also remove all the ones I want (IE. FiscalMonthOfYear 2-12)
Any help or guidance is greatly appreciated!
Thanks!
-Russ
Update:
DimDate table has primary key PKDate, which is one row for every date:
DimDate
PKDate ....
2014-07-01
2014-07-02
2014-07-03
etc.
FaceSales table has one ore many Sales transactions for a given day:
FactSales
SaleDate Amount
2014-07-01 34.99
2014-07-01 21.89
2014-07-02 24.77
2014-07-04 22.77
The problem is that FactSales may not have a sale on a particular day. So my query is finding that one (or many) days with no transactions, and because of the LEFT JOIN is returning it. How would I go about removing this result so it's not in my results?
SELECT
d.PKDate
,f.SaleDate
FROM
DimDate d
LEFT JOIN FactSales f on f.SaleDate=d.PKDate
LEFT JOIN DimPerson p on p.PersonId=f.PersonId
WHERE d.FiscalYear='2014/7/1'
ORDER BY d.PKDate

Answer 1

The problems stems from the fact that you are actually trying to do two things at once:
You want all the Names related to sales of fiscal months with at
least one sale
You want an extra row for all fiscal month with no
sales
As often goes in these cases... you should solve the two distinct problems and then put together the results (with a UNION in this specific case).
Something like this:
SELECT * FROM
(
SELECT DISTINCT
d.FiscalMonth,
d.FiscalMonthOfYear,
p.Name
FROM DimDate d
JOIN FactSales f ON f.SaleDate=d.PKDate
JOIN DimPerson p ON p.PersonId=f.PersonId
WHERE d.FiscalYear='2014/7/1'
) UNION (
SELECT
d.FiscalMonth,
d.FiscalMonthOfYear,
NULL AS Name
FROM DimDate d
LEFT JOIN FactSales f ON f.SaleDate=d.PKDate
WHERE d.FiscalYear='2014/7/1'
GROUP BY d.FiscalMonth, d.FiscalMonthOfYear, p.Name
HAVING COUNT(f.SaleDate)=0
)
ORDER BY FiscalMonthOfYear asc, PersonID ASC
I haven't tested it, and there may be some better ways to solve the second part (SUBSELECT, EXISTS) but that depends a bit on the engine you are using.

Answer 2

You can do an inner join as follows:
SELECT
d.FiscalMonth,
d.FiscalMonthOfYear,
p.Name
FROM
DimDate d
INNER JOIN FactSales f on f.SaleDate=d.PKDate
LEFT JOIN DimPerson p on p.PersonId=f.PersonId
WHERE d.FiscalYear='2014/7/1'
group by d.FiscalMonth, d.FiscalMonthOfYear, p.Name
ORDER BY d.FiscalMonthOfYear asc, p.PersonID asc
The inner join does a union of the two tables without giving priority to the left table. For more on joins you can read this blog: Visual representation of sql joins
Which states that an INNER JOIN will return all of the records in the left table (table A) that have a matching record in the right table (table B) whearas a LEFT JOIN will return all of the records in the left table (table A) regardless if any of those records have a match in the right table (table B)