How do this tricky query?

[Dorian]

I have 2 tables, a CASE table and an INVESTIGATOR table.
This is a one-to many relationship. Each Investigator has an Assign Date and
a Completion Date.
There may be zero, one or many investigators per case but only one at a time.

Completion dates could be missing:
Investigator1 Assigned 12/10/09 Completed 12/10/09
Investigator2 Assigned 12/10/09 Completed null
Assigned dates could be the same e.g.
Investigator1 Assigned 12/10/09 Completed 12/10/09
Investigator2 Assigned 12/10/09 Completed 12/11/09
Or, different e.g.
Investigator1 Assigned 12/10/09 Completed 12/11/09
Investigator2 Assigned 12/11/09 Completed 12/11/09
This is theoretically possible, in which case either record could be
returned:
Investigator1 Assigned 12/10/09 Completed 12/10/09
Investigator2 Assigned 12/10/09 Completed 12/10/09

I am trying to come up with a LatestInvestigator query that I can join to
the Case table.

The rule is I need the latest completion date (null being later than any
date) or if all completion dates are the same, the latest assign date or if
all assign/completion dates are the same, any one record.

-- Dorian
"Give someone a fish and they eat for a day; teach someone to fish and they
eat for a lifetime".

 

[John Spencer]

Is there a primary key in the Case table? If so, you could use a query that
looks like the following generic query

SELECT Investigator.*
, Case.*
FROM Investigator INNER JOIN Case
ON Investigator.PrimaryKey = Case.ForeignInvestigatorKey
WHERE Case.PrimaryKey IN
(SELECT TOP 1 C1.PrimaryKey
FROM Case as C1
WHERE C1.ForeignInvestigatorKey = Case.ForeignInvestigatorKey
ORDER BY Nz(C1.Completed,#2999-12-31#) DESC
, C1.Assigned DESC
, C1.PrimaryKey)

John Spencer
Access MVP 2002-2005, 2007-2009
The Hilltop Institute
University of Maryland Baltimore County

 

[Dorian]

Never mind. I fixed it.
-- Dorian
"Give someone a fish and they eat for a day; teach someone to fish and they
eat for a lifetime".

 

[Jeff Boyce]

If you'll post your solution, other folks may be able to benefit from your
(painful) experience... <g>

Regards

Jeff Boyce
Microsoft Access MVP

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[Dorian]

I did something similar to this. Instead of using the assign and completion
dates, I simply used the latest primary key in the Investigator table. It's
an autonumber key and I understand not guaranteed to increment reliably but
it seems to work ok so far and I have other more important things to worry
about.
-- Dorian
"Give someone a fish and they eat for a day; teach someone to fish and they
eat for a lifetime".