避免由 DATE_TRUNC 引起的对 Indexed Group By 排序

有没有办法避免由于函数未被​​识别为索引的一部分而导致的Sort操作？该功能不会真正影响.GROUP BYDATE_TRUNCtstampixix

CREATE INDEX ix ON tbl(col, tstamp, num)

  SELECT col,
         DATE_TRUNC('MONTH', tstamp AT TIME ZONE 'UTC') AS trunc,
         SUM(num)
    FROM tbl
   WHERE col IN (?, ?, ...)
     AND tstamp >= ?
     AND tstamp <  ?
GROUP BY col, trunc

精度参数DATE_TRUNC是动态的，它也可以是'DAY'或'YEAR'……所以如果不为每个变体创建索引，我就无法索引该函数。

我得到的执行计划：

Finalize GroupAggregate
  Group Key: col, DATE_TRUNC('MONTH', tstamp AT TIME ZONE 'UTC')
  ->  Gather Merge
        Workers Planned: 2
        Workers Launched: 2
        ->  Partial GroupAggregate
              Group Key: col, DATE_TRUNC('MONTH', tstamp AT TIME ZONE 'UTC')
              ->  Sort
                    Sort Key: col, DATE_TRUNC('MONTH', tstamp AT TIME ZONE 'UTC')
                    Sort Method: external merge  Disk: ...kB
                    -> Parallel Index Only Scan using ix on tbl
                         Index Cond: ((col = ANY (...)) AND (tstamp >= ...) AND (tstamp < ...))
                         Heap Fetches: 0

我想要的执行计划看起来像这样：

GroupAggregate
  Group Key: col, DATE_TRUNC('MONTH', tstamp AT TIME ZONE 'UTC')
  ->  Index Only Scan using ix on tbl
        Index Cond: ((col = ANY (...)) AND (tstamp >= ...) AND (tstamp < ...))
        Heap Fetches: 0

（如果我不使用，我会明白DATE_TRUNC）