Question

我有一个查询，该查询返回很多行。我需要最后一行和第一行中的值之间的差异。 TimeCol是一个DateTime列，所有其他列的类型均为float。

我当前的（简体）查询是这样：

select 
    timeCol, TotSoap_W1, TotSoap_W2, TotEnergy
from
    TotEnergy
where 
    TimeCol >= '2019-03-01 00:00:00' and timeCol < '2019-03-02 00:00:00'
order by 
    TimeCol asc

Answer 1

这可能不是最好的方法，但应该完成这项工作：

SELECT B.TotSoap_W1-A.TotSoap_W1 as TotSoap_W1, B.TotSoap_W2-A.TotSoap_W2 as TotSoap_W2, B.TotEnergy-A.TotEnergy as TotEnergy
FROM
(select TOP(1) timeCol, TotSoap_W1, TotSoap_W2, TotEnergy
from TotEnergy
where TimeCol >= '2019-03-01 00:00:00' and timeCol < '2019-03-02 00:00:00'
order by TimeCol ASC) A,
(select TOP(1) timeCol, TotSoap_W1, TotSoap_W2, TotEnergy
from TotEnergy
where TimeCol >= '2019-03-01 00:00:00' and timeCol < '2019-03-02 00:00:00'
order by TimeCol DESC
) B

Answer 2

您可以使用FIRST_VALUE和LAST_VALUE分析函数：

select top 1 LAST_VALUE(TotSoap_W1) OVER (ORDER BY TimeCol ROWS
                                          BETWEEN UNBOUNDEDPRECEDING AND UNBOUNDED FOLLOWING)
             - FIRST_VALUE(TotSoap_W1)
from TotEnergy
where TimeCol >= '2019-03-01 00:00:00' and timeCol < '2019-03-02 00:00:00'
order by TimeCol asc

LAST_VALUE根据排序顺序返回每个组/结果集中的最后一个值。在此查询中，这与返回每一行的TotSoap_W1值相同。为了使其返回所有结果中的最后一个值，我们需要添加ROWS BETWEEN UNBOUNDEDPRECEDING AND UNBOUNDED FOLLOWING子句

SQL Server：从第一行减去最后一行

2 个答案: