如何在Postgresql腳本中存儲變量？

Question

我有以下腳本，我需要找到一個給定的章節，改變狀態，然后將其存儲在活動參考以后刪除活動（因為FK在chapter_published活動），刪除chapter_published參考，然后使用id_activity最終刪除父級活動。

我如何以一種非常簡單的方式使用postgresql腳本以編程方式進行此操作？ 並在哪里記錄？

以下是我期望實現的示例：

-- Manually find the chapter I want first
select * from ws_chapter;

-- store the chapter once so I don't have to repeat in each statement
@chapter_id = 15;

-- Update the state field
update chapter set cd_state = 'DRAFT' where id_chapter = @chapter_id;

-- Now get the id of the activity for later use
@activity_id = select id_activity from chapter_published where id_chapter = @chapter_id;

-- Make the delete
delete from chapter_published where id_chapter = @chapter_id;
delete from activity where id_activity = @activity_id;

Answer 1

在這種情況下，您實際上並不需要變量。 您可以通過修改公用表表達式的單個數據來實現：

with updated as (
  update chapter 
      set cd_state = 'DRAFT'
  where id_chapter = 15
  returning id_chapter
), delete_published as (
  delete from chapter_published
  where id_chapter in (select id_chapter from updated)
  returning id_activity
)
delete from activity 
where id_activity in (select id_activity from delete_published);

如果您想使用某種“變量”定義，可以在開始時使用一個CTE來完成：

with variables (chapter_id) as (
   values (15)
), updated as (
   update chapter 
       set cd_state = 'DRAFT'
   where id_chapter = (select chapter_id from variables)
), delete_published as (
 ...
)
...

Answer 2

您可以使用內聯PLPGSQL函數執行此操作：

do $$
declare
    chapter_id int = 15;
begin

    //do stuff;

end $$;

或者在postgresql.conf設置一個名為my的GUC ，然后

set my.chapter_id = 15;

select current_setting('my.chapter_id'); --not typesafe