Question

您好我正在尝试对物种数据库运行查询。我想查询唯一值，但也找到物种最初找到的年份。

到目前为止，我有这个：

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.";

我正在连接Genus和物种名称并从两个不同的表中添加数据（因此是UNION）。这提供了物种清单，但我想知道在这个地方看到物种的年份。

Answer 1

我猜测你的源表都包含一个日期/时间字段，用于存储每次观察的日期。如果是这样，您可以{2}表格中的UNION数据，并将其用作GROUP BY查询中的子查询来源，在该查询中，您可以得出每个物种的最小观察年份。

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;

MS Access SQL查找值首次出现的年份

1 个答案: