我正在尝试将 postgresql 查询转换为 plr 函数

Question

我有一个postgres 查询，当我将它作为查询运行时，它运行良好。但是，我想将其转换为pl/r 并能够动态输入开始和结束日期。

有效的 SQL 是：

with date as (
select d as first_day,
d + interval '1 month' - interval '1 day' as last_day
from generate_series('2010-01-01'::date,
                     '2018-12-01'::date,
                     '1 month') as d
) select last_day::date as snapshot_date from date;

想做一个 pl/r like:

DROP FUNCTION IF EXISTS standard.seq_monthly(min_date_str char, max_date_str char);
CREATE FUNCTION standard.seq_monthly(min_date_str char, max_date_str char)
RETURNS setof dates AS
$$ 
with date as (
select d as first_day,
d + interval '1 month' - interval '1 day' as last_day
from generate_series(min_date_str::date,
                     max_date_str::date,
                     '1 month') as d
) select last_day::date as snapshot_date from date;

$$
LANGUAGE 'plr';
select * from standard.seq_monthly('2010-01-01' , '2018-12-01')

但是，我在运行该函数时遇到了错误。错误是

在“PLR711818

已尝试将最大最小日期也声明为日期。

非常感谢任何帮助。

Answer 1

PL/R 是 PostgreSQL 中的 procedural language 扩展（类似于 plpython、plperl、plphp），可以在其中运行有效、兼容的 R 语言代码。您正在尝试的 SQL 本身不能在 R 会话中运行，因此您的代码将在 PG plr 存储函数中失败。

但是，不需要这样的扩展，因为您可以使用非常基本的 SQL 语言（通常效率更高）来处理您的需求，以按指定的输入范围返回所需的日期范围表：

CREATE OR REPLACE FUNCTION seq_monthly(min_date_str char, max_date_str char)
RETURNS TABLE(snapshot_date date) AS
$$ 
     with mydate as (
          select d as first_day,
                 DATE_TRUNC('month', d) 
                     + '1 MONTH'::INTERVAL 
                     - '1 DAY'::INTERVAL as last_day
          from generate_series(min_date_str::date,
                               max_date_str::date,
                               '1 month') as d
     ) 

     select last_day::date as snapshot_date from mydate;

$$
LANGUAGE SQL STABLE;

select * from seq_monthly('2010-01-31' , '2018-12-31');

Rextester demo

---

现在，如果您真的想要 plr 存储函数，请在给定日期范围内使用 R 的 seq()：

CREATE FUNCTION standard.seq_monthly(min_date_str char, max_date_str char)
RETURNS setof dates AS
$$ 
    seq(as.Date(min_date_str), as.Date(max_date_str), by='month')
$$
LANGUAGE 'plr';

select * from standard.seq_monthly('2010-01-01' , '2018-12-01')

Answer 2

其中一种解决方法是不走plr，而是写一个sql查询：

with max_min_date as(
select max(snapshot_date) as max_date_str, min(snapshot_date) as min_date_str from data
) , 
ts as (
select d as first_day,
d + interval '1 month' - interval '1 day' as last_day
from generate_series((select min_date_str from max_min_date)::date,
                     (select max_date_str from max_min_date)::date,
                     '1 month') as d
) select last_day::date as snapshot_date from ts;

如果您需要月末日期而不是月初：

with max_min_date as(
  with max_min_wrk as (
    select max(snapshot_date) as max_date_str, min(snapshot_date) as min_date_str from data
    ) select cast(date_trunc('month', max_date_str) as date) as max_date, cast(date_trunc('month', min_date_str) as date) as min_date from max_min_wrk
), 
ts as (
select d as first_day,
d + interval '1 month' - interval '1 day' as last_day
from generate_series((select min_date from max_min_date)::date,
                     (select max_date from max_min_date)::date,
                     '1 month') as d
) select last_day::date as snapshot_date from ts 
order by snapshot_date asc;