如何在 PostgreSQL 查询中声明变量 [重复]

Posted 2023-03-22

【中文标题】如何在 PostgreSQL 查询中声明变量 [重复]

【英文标题】：How to declare a variable in PostgreSQL queries [duplicate]

【发布时间】：2017-04-21 02:14:36

【问题描述】：

我正在努力在 PostgreSQL 查询中声明变量。谁能帮我解决以下问题？

declare CampaignID val INT;
select CampaignID = 6
select
    result_code.description,
    count (*) as count
from 
    history
        left join result_code on result_code.result_code = history.result_code
where
    campaign_id = CampaignID
        and history.start_date_time between '2016-12-06 00:00:00' and '2016-12-06 23:00:00'
group by
    result_code.description

【参考方案1】：

1) 第一种方式（带有PL/pgSQL函数）：

CREATE OR REPLACE FUNCTION MY_SELECT_FUNC(CampaignID integer)
RETURNS TABLE(res_description character varying(255), res_count integer) AS
$BODY$
BEGIN

  for res_description, res_count
  in
  select
    result_code.description,
    count (*) as count
  from history
    left join result_code on result_code.result_code = history.result_code
  where campaign_id = CampaignID
    and history.start_date_time between '2016-12-06 00:00:00' and '2016-12-06 23:00:00'
  group by result_code.description
  loop
    return next;
  end loop;

END;$BODY$
LANGUAGE plpgsql VOLATILE;

然后你可以在sql中选择结果：

SELECT * from MY_SELECT_FUNC(6);

2) 第二种方式（带sql函数）：

CREATE TYPE MY_SELECT_FUNC_RES AS (res_description character varying(255), res_count integer);

CREATE OR REPLACE FUNCTION MY_SELECT_FUNC(CampaignID integer)
RETURNS SETOF MY_SELECT_FUNC_RES AS
$$
  select
    result_code.description,
    CAST(count(*) AS INTEGER)
  from history
    left join result_code on result_code.result_code = history.result_code
  where campaign_id = CampaignID
    and history.start_date_time between '2016-12-06 00:00:00' and '2016-12-06 23:00:00'
  group by result_code.description
$$
LANGUAGE SQL;

然后你可以在sql中选择结果：

SELECT * from MY_SELECT_FUNC(6);