MS Access SQL find the year a value first appears - sql

Question

Hi I'm trying to run a query on a species database. I want to query unique values but also find the year that species was first found.
So far I have this:
SELECT DISTINCT [Genus_HeTR] & " " & [Species_HeTR] AS Species
FROM HeTR_Rec
WHERE [Species_HeTR] <> "sp."
UNION SELECT DISTINCT [Genus_HeOP] & " " & [Species_HeOP] AS Species
FROM HeOP_Rec
WHERE [Species_HeOP] <> ""
AND [Species_HeOP] <> "sp.";
I'm concatenating the Genus and species name and adding data from two different tables (hence the UNION). This provides a species list but I would like to know the year that species was seen at this site.

Answer 1

I will hazard a guess that both your source tables include a Date/Time field which stores the date of each observation. If that is so, you can UNION data from the 2 tables and use that as a subquery source in a GROUP BY query where you derive the minimum observation year for each species.
SELECT
sub.Species,
Min(sub.observation_year) AS first_sighting_year
FROM
(
SELECT
[Genus_HeTR] & " " & [Species_HeTR] AS Species,
Year(observation_date) AS observation_year
FROM HeTR_Rec
WHERE [Species_HeTR] <> "sp."
UNION ALL
SELECT
[Genus_HeOP] & " " & [Species_HeOP] AS Species,
Year(observation_date) AS observation_year
FROM HeOP_Rec
WHERE [Species_HeOP] <> ""
AND [Species_HeOP] <> "sp."
) AS sub
GROUP BY sub.Species;