PostgreSQL 外鍵違規內部交易

Question

我有一個 function 里面有幾個查詢，如下所示：

CREATE OR REPLACE FUNCTION public.myfunction(winningid integer, losingid integer)
 RETURNS void
 LANGUAGE plpgsql
AS $function$
begin

update partecipants set id_be=winningId where id_be=losingId;
...
many other updates and deletes regarding other tables
...

delete from business_entity where id_be=losingId;

end;
$function$
;

參與者和business_entity之間有一個外鍵：

ALTER TABLE partecipants ADD CONSTRAINT partecipants_fk FOREIGN KEY (id_be) REFERENCES business_entity(id_be)

有時（如千分之一）此 function 掛起並出現錯誤：

error: update or delete on table "business_entity" violates foreign key constraint "partecipants_fk" on table "partecipants"
detail:
   'Key (id_be)=(315017) is still referenced from table "partecipants".

如果我第二次運行相同的 function ，則結束沒有錯誤。

這怎么可能？

作為背景信息，其他進程在運行時正在使用（通常也帶有鎖）function 中涉及的表。

Answer 1

並發事務可以在您的UPDATE和您的DELETE之間添加或修改partecipants中的行，以便后者失敗。

如果您想避免這種情況，請在一個語句中執行這兩項操作：

WITH dummy AS (
   update partecipants set id_be=winningId where id_be=losingId
)
delete from business_entity where id_be=losingId;