SQL-两个字段之间的最大和最小时间变化 [英] SQL - Max and Min time between two fields changing

问题描述

我有一个包含两列的PL/SQL表:log_date(DATE)和value(FLOAT).数据非常细粒度，log_dates之间的差异可能是几毫秒. value随时间变化.我想使用SQL查找value增加所需的log_date s之间的最大和最小时间.

I have a PL/SQL table with two columns: log_date (DATE) and value (FLOAT). The data is very fine-grained, the difference between log_dates could be a few milliseconds. The value changes over time. I want to find, using SQL, the maximum and minimum amount of time between log_dates it takes for value to increase.

示例

log_date | value
-------------------  
  15:00  |  10
  15:01  |  10
  15:02  |  11
  15:03  |  11
  15:04  |  11
  15:05  |  11
  15:06  |  12

在15:00和15:02之间value增加了，但是在15:03和15:06之间也增加了，这花费了更长的时间，所以我想要一个查询，该查询将返回(在这种情况下)"3分钟"(作为DATE或NUMBER)-value增加所需的最长时间.

Between 15:00 and 15:02 value increased BUT it also increased between 15:03 and 15:06 which took longer, and so I want a query that would return (in this case) '3 minutes' (as a DATE or a NUMBER) - the longest amount of time it took for value to increase.

推荐答案

我可以在T-SQL中给您答案，但是我不确定您使用的是哪种方言. TBH，这是我们首先想到的一个循环(其他人可能有更好的方法！):

I can give you an answer in T-SQL, but I'm not sure what dialect you're using. TBH, a loop here is the first thing that springs to mind (someone else may have a better way of doing it!):

DECLARE @temp TABLE ( log_date DATETIME, value FLOAT )
INSERT INTO @temp ( log_date, value ) SELECT log_date, value FROM <MyTableName>

DECLARE @diff TABLE ( time_diff INT, old_value FLOAT, new_value FLOAT )

-- the loop

DECLARE @prev_value FLOAT, 
        @cur_value FLOAT,
        @prev_log_date DATETIME,
        @cur_log_date DATETIME

WHILE EXISTS ( SELECT NULL FROM @temp )
BEGIN

    SELECT TOP 1 @cur_log_date = log_date, @cur_value = value
    FROM @temp
    ORDER BY log_date

    IF ( @prev_value IS NOT NULL AND @prev_log_date IS NOT NULL )
    BEGIN

        INSERT INTO @diff ( time_diff, old_value, new_value )
        SELECT DATEDIFF('ms', @prev_log_date, @cur_log_date ),
               @prev_value, @cur_value

    END

    SELECT @prev_log_date = @cur_log_date, @prev_value = @cur_value
    DELETE FROM @temp WHERE log_date = @cur_log_date

END

SELECT MAX(time_diff), MIN(time_diff) FROM @diffs

这样，您最终得到一个包含所有差异的表，然后可以查询该表.

This way, you end up with a table of all differences that you can then query.

HTH

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