选择每个月的最大日期

Question

I have a table with a lot of cumulative columns, these columns reset to 0 at the end of each month. If I sum this data, I'll end up double counting. Instead, With Hive, I'm trying to select the max date of each month.

I've tried this:

SELECT
    yyyy_mm_dd,
    id,
    name,
    cumulative_metric1,
    cumulative_metric2
FROM
    mytable

WHERE
    yyyy_mm_dd = last_day(yyyy_mm_dd)

mytable has daily data from the start of the year. In the output of the above, I only see the last date for January but not February. How can I select the last day of each month?

Answer 1

February is not over yet. Perhaps a window function does what you want:

SELECT yyyy_mm_dd, id, name, cumulative_metric1, cumulative_metric2
FROM (SELECT t.*,
             MAX(yyyy_mm_dd) OVER (PARTITION BY last_day(yyyy_mm_dd)) as last_yyyy_mm_dd
      FROM mytable t
     ) t
WHERE yyyy_mm_dd = last_yyyy_mm_dd;

This calculates the last day in the data .

Answer 2

use correlated subquery and date to month function in hive

SELECT
    yyyy_mm_dd,
    id,
    name,
    cumulative_metric1,
    cumulative_metric2
FROM
    mytable t1

WHERE
    yyyy_mm_dd = select max(yyyy_mm_dd) from mytable t2 where
     month(t1.yyyy_mm_dd)= month(t2.yyyy_mm_dd)