BigQuery标准SQL：如何获取两列之间的差异中位数？

Question

How can I get the median difference after subtracting two columns in a table after I set the dialect to Standard SQL ?

These are the things that I have tried and failed with:

SELECT
  symbol,
  median(max_height-min_height)
FROM
  `body_table-1345.bodies.heights`
WHERE
  symbol = 'mouse_1344'
  AND max_height> 0
  AND min_height> 0
  AND (measure_date> '2017-11-01 08:45:00.000 UTC'
    AND measure_date< '2017-11-30 17:00:00.000 UTC')
GROUP BY
  symbol

but I get the error Error: Function not found: median at [3:3]

The following works with Legacy SQL but not with Standard SQL :

SELECT
  symbol,
  NTH(501, QUANTILES(max_height-min_height, 1001))
FROM
  `body_table-1345.bodies.heights`
WHERE
  symbol = 'mouse_1344'
  AND max_height> 0
  AND min_height> 0
  AND (measure_date> '2017-11-01 08:45:00.000 UTC'
    AND measure_date< '2017-11-30 17:00:00.000 UTC')
GROUP BY
  symbol

The columns I'd like to subtract are max_height and min_height .

Answer 1

Instead, you can use a slight variation of ANSI standard percentile functions.

SELECT DISTINCT symbol,
       percentile_cont(max_height-min_height, 0.5) over (partition by symbol )
FROM `body_table-1345.bodies.heights`
WHERE symbol = 'mouse_1344' AND
      max_height > 0 AND
      min_height > 0 AND
      (measure_date> '2017-11-01 08:45:00.000 UTC' AND
       measure_date< '2017-11-30 17:00:00.000 UTC'
      );

Unfortunately, this is one of the analytic functions that is only available as an analytic function and not as an aggregation function. Hence, the SELECT DISTINCT syntax rather than GROUP BY .