Question

我正在尝试执行以下SQL：

SELECT * FROM Table2
INNER JOIN
    (SELECT * FROM Table1
    INNER JOIN
    (SELECT MAX(DateTime) AS LastMeasurement, MeasurementId as LastMeasurementId
    FROM Table1 GROUP BY MeasurementId) as lastMeasurement
    ON (Table1.MeasurementId = lastMeasurement.LastMeasurementId) 
    AND (Table1.DateTime = lastMeasurement.LastMeasurement)) as hLastMeasurement
ON Table2.Id = hLastMeasurement.Id
ORDER BY Table2.Id ASC

这很好用，但是因为我想以XML格式获得结果并且不得不投射地理列，所以我将第一行更改为：

SELECT Name, Description, CAST(Location as nvarchar(MAX)) FROM Table2

并将此行添加到最后：

FOR XML RAW ('Object'), ROOT ('Objects'), ELEMENTS

现在我正在获取XML，但仅使用表2中的数据欢迎任何建议。

Answer 1

显然，如果要显示其他表中的数据，则必须以这种方式选择这些列。 IO通常使用MYSQL，因此这是我通常使用的方式。但是如果您使用的是oracle或其他数据库，那么您必须选择正确的别名来显示您希望的自定义列。请参阅使用sql server {{的连接的基本示例3}}

SELECT Table2.Name,Table2.Description,lastMeasurement.MeasurementId 

FROM Table2 t2
    INNER JOIN
        (SELECT * FROM Table1
        INNER JOIN
        (SELECT MAX(DateTime) AS LastMeasurement, MeasurementId as LastMeasurementId
        FROM Table1 GROUP BY MeasurementId) as lastMeasurement
        ON (Table1.MeasurementId = lastMeasurement.LastMeasurementId) 
        AND (Table1.DateTime = lastMeasurement.LastMeasurement)) as hLastMeasurement
    ON Table2.Id = hLastMeasurement.Id
    ORDER BY Table2.Id ASC

从两个表中选择一个XML

1 个答案: