PostgreSQL - 来自同一函数调用的多个聚合查询

Question

我有一个从表中返回setof的函数：

CREATE OR REPLACE FUNCTION get_assoc_addrs_from_bbl(_bbl text)
RETURNS SETOF wow_bldgs AS $$
  SELECT bldgs.* FROM wow_bldgs AS bldgs
  ...
$$ LANGUAGE SQL STABLE;

这是表格将返回的样本：

现在我正在写一个＆＃34;聚合＆＃34;函数将只返回一行，该行包含有关此函数返回的表的各种（聚合）数据点。这是我当前的工作（和天真）示例：

SELECT 
  count(distinct registrationid) as bldgs,
  sum(unitsres) as units,
  round(avg(yearbuilt), 1) as age,
  (SELECT first(corpname) FROM (
    SELECT unnest(corpnames) as corpname
    FROM get_assoc_addrs_from_bbl('3012380016')
    GROUP BY corpname ORDER BY count(*) DESC LIMIT 1
  ) corps) as topcorp,
  (SELECT first(businessaddr) FROM (
    SELECT unnest(businessaddrs) as businessaddr
    FROM get_assoc_addrs_from_bbl('3012380016')
    GROUP BY businessaddr ORDER BY count(*) DESC LIMIT 1
  ) rbas) as topbusinessaddr
FROM get_assoc_addrs_from_bbl('3012380016') assocbldgs

正如您所看到的，对于两个＆＃34;子查询＆＃34;需要自定义分组/排序方法，我需要重复调​​用get_assoc_addrs_from_bbl()。理想情况下，我正在寻找一种可以避免重复调用的结构，因为该函数需要大量处理，并且我希望能够容纳任意数量的子查询。我已经研究过CTE和窗口表达式等，但没有运气。

任何提示？谢谢！

Answer 1

创建简单的aggregate function：

create aggregate array_agg2(anyarray) (
  sfunc=array_cat,
  stype=anyarray);

它将数组值聚合为一个单一的dim数组。例如：

# with t(x) as (values(array[1,2]),(array[2,3,4])) select array_agg2(x) from t;
┌─────────────┐
│ array_agg2  │
╞═════════════╡
│ {1,2,2,3,4} │
└─────────────┘

之后，您的查询可以重写为

SELECT 
  count(distinct registrationid) as bldgs,
  sum(unitsres) as units,
  round(avg(yearbuilt), 1) as age,
  (SELECT first(corpname) FROM (
    SELECT * FROM unnest(array_agg2(corpnames)) as corpname
    GROUP BY corpname ORDER BY count(*) DESC LIMIT 1
  ) corps) as topcorp,
  (SELECT first(businessaddr) FROM (
    SELECT * FROM unnest(array_agg2(businessaddrs)) as businessaddr
    GROUP BY businessaddr ORDER BY count(*) DESC LIMIT 1
  ) rbas) as topbusinessaddr
FROM get_assoc_addrs_from_bbl('3012380016') assocbldgs

（当然，如果我正确理解你的目标）