使用 CASE 和 generate_series() 查询，将结果 timestamptz 降序排列

Question

我是新手，正在尝试使用以下代码创建函数：

CREATE OR REPLACE FUNCTION public.get_bulan()
returns table (request_detail timestamp with time zone)
language plpgsql stable
as $function$
        begin
        return query

        select
        case
        when (extract(DAY FROM now()) >= 25) then generate_series(date_trunc('year', now()), date_trunc('day', now()) ,interval '1 month')
        when (select extract(month FROM now()) = 2) then now() - (interval '1' month * generate_series(0,1))
        when (select extract(month FROM now()) = 1) then now() - (interval '1' month * generate_series(0,2))
        else generate_series((select date(date_trunc('year', now()))), (select date(now())-'1 month'::interval), interval '1 month')
        end
        order by timetstamptz(request_detail) desc;
        end;
        $function$;

上面查询的结果是：

2017-01-01 00:00:00
2017-02-01 00:00:00
2017-03-01 00:00:00
2017-04-01 00:00:00
2017-05-01 00:00:00
2017-06-01 00:00:00
2017-07-01 00:00:00

我尝试使用 order by desc 和 order by timestamp desc 但它不起作用。我想按降序排列，所以我得到了从 2017-07-01 到 2017-01-01 的结果。我该怎么做？

Answer 1

 select
        (case 
        when (extract(DAY FROM now()) >= 25) then generate_series(date_trunc('year', now()), date_trunc('day', now()) ,interval '1 month')
        when (select extract(month FROM now()) = 2) then now() - (interval '1' month * generate_series(0,1))
        when (select extract(month FROM now()) = 1) then now() - (interval '1' month * generate_series(0,2))
        else generate_series((select date(date_trunc('year', now()))), (select date(now())-'1 month'::interval), interval '1 month')
        end) as time_st  order by time_st desc

输出：

2017-07-01 00:00:00+05:30
2017-06-01 00:00:00+05:30
2017-05-01 00:00:00+05:30
2017-04-01 00:00:00+05:30
2017-03-01 00:00:00+05:30
2017-02-01 00:00:00+05:30
2017-01-01 00:00:00+05:30

Answer 2

您有两种方法可以做到这一点：

添加as result_timestamp order by result_timestamp desc;

CREATE OR REPLACE FUNCTION public.get_bulan()
 returns table (request_detail timestamp with time zone)
 language plpgsql stable
 as $function$
    begin
    return query

    select 
    case
    when (extract(DAY FROM now()) >= 25) then generate_series(date_trunc('year', now()), date_trunc('day', now()) ,interval '1 month')
    when (select extract(month FROM now()) = 2) then now() - (interval '1' month * generate_series(0,1))
    when (select extract(month FROM now()) = 1) then now() - (interval '1' month * generate_series(0,2))
    else generate_series((select date(date_trunc('year', now()))), (select date(now())-'1 month'::interval), interval '1 month')
    end as result_timestamp order by result_timestamp desc;

    end;
    $function$;

或者当你从其他地方调用它时，你可以从过程和订单中删除排序：

CREATE OR REPLACE FUNCTION public.get_bulan()
returns table (request_detail timestamp with time zone)
language plpgsql stable
as $function$
        begin
        return query

        select 
        case
        when (extract(DAY FROM now()) >= 25) then generate_series(date_trunc('year', now()), date_trunc('day', now()) ,interval '1 month')
        when (select extract(month FROM now()) = 2) then now() - (interval '1' month * generate_series(0,1))
        when (select extract(month FROM now()) = 1) then now() - (interval '1' month * generate_series(0,2))
        else generate_series((select date(date_trunc('year', now()))), (select date(now())-'1 month'::interval), interval '1 month')
        end;

        end;
        $function$;

并调用：

select request_detail from public.get_bulan() order by request_detail desc

注意：第二个非常柔韧，您可以轻松操作。

Answer 3

您的 SQL CASE 语句的第一个和最后一个分支 return 行按降序排列，其他两个按升序排列。因此，您需要在外部 SELECT.

中添加另一个 ORDER BY

彻底的解决方法是使所有 4 个分支 return 行的顺序相同。

或者更确切地说，完全重写它以理清混乱：

SELECT *
FROM   generate_series(
         CASE
            WHEN extract(DAY   FROM now()) >= 25 THEN date_trunc('month', now())
            WHEN extract(MONTH FROM now()) <=  2 THEN now()
            ELSE                                      now() - interval '1 month'
         END
       , date_trunc('year' , now())
       , interval '- 1 month'  -- negative interval
      ) t(request_detail)
ORDER  BY request_detail DESC;  -- redundant

负区间自动降序排列。您可以添加 ORDER BY request_detail DESC 以明确和正确标准 SQL.

如果愿意，可以将查询包装到一个函数中。

最重要的是，不要将 set-returning 函数像 generate_series() 包装在 CASE语句。这从来都不是一个好主意，但从 Postgres 10 开始它会引发错误：

ERROR:  set-returning functions are not allowed in CASE

演示：

dbfiddle here

使用 CASE 和 generate_series() 查询，将结果 timestamptz 降序排列

Query with CASE and generate_series(), order resulting timestamptz descending

sql

postgresql

sql-order-by

plpgsql

set-returning-functions