plpgsql - 不同形式的临时表以进行排序

Question

我正在尝试优化具有 7 个 WITH 临时表的函数，充当排序机制，从初始临时表/排序级联到下一个直到最后一个，例如第 7 个临时表/排序。

Gist here：这种代码一定要禁止。

我正在尝试将 WITH 排序替换为真正的临时表，例如 CREATE TEMPORARY TABLE <table_name> AS SELECT col1 FROM another_table;。目的是提高性能，因为当前形式的查询非常非常慢。

这是我提出的改变

CREATE OR REPLACE FUNCTION report.get_sa001(
  IN "date_D" timestamp without time zone,
  IN "date_F" timestamp without time zone,
  IN frequence integer)
RETURNS TABLE(
  "Period_date" timestamp without time zone, 
  "Site" character varying, 
  "Customer_code" character varying, 
  "Internal_reference" character varying, 
  "InvoiceNumber" character varying, 
  "Value_in_currency" numeric, 
  "Value_in_EUR" numeric, 
  "Value_Budget_in_EUR" numeric, 
  "Selling_price_CUR" numeric, 
  "Selling_price_EUR" numeric, 
  "Currency_code" character varying, 
  "Selling_quantity" numeric, 
  "Variance_price_CUR" numeric, 
  "Variance_price_EUR" numeric, 
  "Variance_value_CUR" numeric, 
  "Variance_value_EUR" numeric, 
  "Selling_date" timestamp without time zone) AS

$BODY$
DECLARE
  p_debut timestamp without time zone;
DECLARE
  p_fin timestamp without time zone;
BEGIN
  p_debut = dw.get_period_end("date_D", "frequence");
  p_fin = dw.get_period_end("date_F", "frequence");

  RETURN QUERY 
    CREATE TEMPORARY TABLE "dates_1" AS
      SELECT
        p_debut::date + n AS "date",
        dw.period_frequency(p_debut::date + n) AS "frequency"               
      FROM generate_series(0, p_fin::date - p_debut::date) AS x(n)
      WHERE (dw.period_frequency(p_debut::date + n) & frequence != 0);

  SELECT * FROM "dates_1"; -- Thanks to Vao Tsun
END;
$BODY$
  LANGUAGE plpgsql STABLE
  COST 100
  ROWS 1000;

函数的创建很好，但是以这种方式运行函数时

SELECT * FROM report.get_sa001('2017-01-01'::date, '2017-01-31'::date, 32)

这就是我所拥有的

 ERROR: cannot open query CREATE TABLE AS like cursor
 État SQL :42P11
 Contexte : fonction PL/pgsql report.get_sa001(timestamp without time  zone,timestamp without time zone,integer), ligne 11 à RETURN QUERY

我尝试将CREATE TEMPORARY TABLE 替换为SELECT * INTO TEMPORARY TABLE。再次创建正常，但运行时出现相同的错误。

检查 SO 的存档，听起来 PLPGSQL 禁止使用临时表（检查 here）。

如果您有任何想法，我们非常欢迎。

谢谢

Answer 1

在函数中使用创建临时表没有任何问题：

t=# create or replace function so37() returns table (i int) as
$$
declare
begin
create temporary table a as select 2;
return query select * from a;
end;
$$ language plpgsql
;
CREATE FUNCTION
t=# select * from so37();
 i
---
 2
(1 row)

但必须维护它们，例如在您当前的示例中，如果存在则缺少删除表，或者您应该插入而不是创建表，因为如果不这样做，第二次运行将失败：

t=# select * from so37();
ERROR:  relation "a" already exists
CONTEXT:  SQL statement "create temporary table a as select 2"
PL/pgSQL function so37() line 4 at SQL statement

而且我相信 CTE 是在函数中创建临时表的更好选择...