MS-Access Including all days in a Date Range Query

Question

Access 2010 here.

Back with another puzzler. I have this query:

SELECT DischargeDatabase.Date, Avg([pH]) AS [pH Value], Avg([Temperature]) AS [Temperature (°C)], Avg([ZincLevel]) AS [Zinc (mg/l)], Sum([Effluent]) AS [Discharge (gal)], Count(*) AS [# Discharges]
FROM DischargeDatabase
WHERE DischargeDatabase.Date Between Forms!QueryForm!TextCriteriaQ0A And Forms!QueryForm!TextCriteriaQ0B
GROUP BY DischargeDatabase.Date;

from a waste water treatment database that I've been building. This gives a by-day summary of waste water discharges, averaging the pH, Temperature, and zinc levels, and summing the discharge volume (effluent). The user selects a range in two text boxes on the "QueryForm" with date pickers, and runs the query.

What is shown is discharges, grouped by day, for the date range, and only days that had discharges are listed. What a user has requested is for every day in the range selected to be shown, and those days without records in the "DischargeDatabase" just have zeros for the field values.

i.e. from this (date range 4/11/2013 to 4/16/2013, over a weekend):

Date      | ph Value | Temperature (°C) | Zinc (mg/l) | Discharge (gal) | # Discharges
4/11/2013   9.5        18.6               0.89          5000              5
4/12/2013   9.1        17.9               1.68          3000              2
4/15/2013   8.9        19.6               1.47          10000             7
4/16/2013   9.6        18.2               0.35          1500              1

to this:

Date      | ph Value | Temperature (°C) | Zinc (mg/l) | Discharge (gal) | # Discharges
4/11/2013   9.5        18.6               0.89          5000              5
4/12/2013   9.1        17.9               1.68          3000              2
4/13/2013   0.0         0.0               0.0           0                 0
4/14/2013   0.0         0.0               0.0           0                 0
4/15/2013   8.9        19.6               1.47          10000             7
4/16/2013   9.6        18.2               0.35          1500              1

This is all so that the user can paste the query into an excel spreadsheet without issue. I'm not even sure that this is possible, or within the scope of a query (you are "selecting" records that don't exist). What might work is some sort of join with a bogus table/query pre-filled with zeros?

Thank you for the help and any ideas!

Answer 1

This could be fairly easy with a calendar table. You can build your own using custom CreateTable_calendar and LoadCalendar procedures.

Create a query which filters the calendar table based the the date range and LEFT JOIN it to your other table. (I simplified the SELECT field list in this example.)

SELECT
    c.the_date,
    Count(ddb.Date) AS [# Discharges]
FROM
    tblCalendar AS c
    LEFT JOIN DischargeDatabase AS ddb
    ON c.the_date = ddb.Date
WHERE
    c.the_date Between
            Forms!QueryForm!TextCriteriaQ0A
        And Forms!QueryForm!TextCriteriaQ0B
GROUP BY c.the_date;

Answer 2

You are on the right track with your last statement! This kind of thing - fill all the groups even when there is no data - can be done with what we call a numbers table or tally table, which can be a CTE, or a real table, whatever you want to do. You can expand the CTE to generate dates...

;WITH CTE AS (
  SELECT 1 as Num
  UNION ALL
  SELECT Num + 1 FROM CTE WHERE Num < @Max
)

SELECT * FROM CTE

This pattern can be expanded to generate your dates...

declare @startDate datetime
set @startDate = getdate() --to start from today

;WITH CTE AS (
  SELECT @startDate as myDate
  UNION ALL
  SELECT dateadd(day, 1, myDate) as myDate FROM CTE WHERE myDate < dateadd(day, 30, @startDate)
)

SELECT myDate FROM CTE

Now, you can use that CTE as the left table in a right outer join. In Access, I think this will need to be a real table. Just create one and manually populate it with numbers - you only have to do this one time.