存在外键时违反外键约束答案

【问题标题】：Foreign key constraint violation when foreign key is present存在外键时违反外键约束
【发布时间】：2014-10-24 05:00:19
【问题描述】：

我是 PostgreSQL 和一般数据库的新手，我试图弄清楚为什么即使存在外键，我也会遇到外键违规。

我运行的查询

insert into analytics_url_redirect
(source, news_item_id, access_date)
select 'n',id,CURRENT_TIMESTAMP from entry_entry_master
where id=43068778;

这失败了

ERROR: insert or update on table "analytics_url_redirect" violates foreign key constraint "news_item_id_refs_id_15ddd78c"
SQL state: 23503
Detail: Key (news_item_id)=(43068778) is not present in table "entry_entry_master".

以下选择查询也可以正常工作并返回 43068778：

select id  from entry_entry_master where id=43068778;

整个create table命令——django sqlall的输出是

BEGIN;
CREATE TABLE "analytics_url_redirect" (
    "id" serial NOT NULL PRIMARY KEY,
    "newsletter_id" integer REFERENCES "nlc_newsletter" ("newslettercore_ptr_id") DEFERRABLE INITIALLY DEFERRED,
    "alert_id" integer REFERENCES "alerts_emailtracker" ("id") DEFERRABLE INITIALLY DEFERRED,
    "source" varchar(1) NOT NULL,
    "brief_id" integer REFERENCES "brief_brief" ("id") DEFERRABLE INITIALLY DEFERRED,
    "news_item_id" integer REFERENCES "entry_entry_master" ("id") DEFERRABLE INITIALLY DEFERRED,
    "external_news_item_id" integer REFERENCES "nlc_newsletterblock" ("id") DEFERRABLE INITIALLY DEFERRED,
    "recipient_id" integer REFERENCES "subscriber_subscriber" ("id") DEFERRABLE INITIALLY DEFERRED,
    "external_recipient_id" integer REFERENCES "subscriber_pseudosubscriber" ("id") DEFERRABLE INITIALLY DEFERRED,
    "access_date" timestamp with time zone NOT NULL
)
;
CREATE INDEX "analytics_url_redirect_newsletter_id" ON "analytics_url_redirect" ("newsletter_id");
CREATE INDEX "analytics_url_redirect_alert_id" ON "analytics_url_redirect" ("alert_id");
CREATE INDEX "analytics_url_redirect_brief_id" ON "analytics_url_redirect" ("brief_id");
CREATE INDEX "analytics_url_redirect_news_item_id" ON "analytics_url_redirect" ("news_item_id");
CREATE INDEX "analytics_url_redirect_external_news_item_id" ON "analytics_url_redirect" ("external_news_item_id");
CREATE INDEX "analytics_url_redirect_recipient_id" ON "analytics_url_redirect" ("recipient_id");
CREATE INDEX "analytics_url_redirect_external_recipient_id" ON "analytics_url_redirect" ("external_recipient_id");
CREATE INDEX "analytics_url_redirect_access_date" ON "analytics_url_redirect" ("access_date");
COMMIT;

那么当外键存在时，怎么可能违反外键约束呢？我错过了什么明显的东西吗？

【问题讨论】：

这确实很奇怪。您可以尝试重新索引entry_entry_master 表（或至少该表中id 上的索引）吗？

标签： sql database postgresql foreign-key-relationship

【解决方案1】：

这是我自己想出来的。 :(

我错过的一个细节是 entry_entry_master 是使用表继承进行分区的。来自 postgres 文档：postgres Inheritance

继承特性的一个严重限制是索引（包括唯一约束）和外键约束仅适用于单个表，而不适用于它们的继承子表。在外键约束的引用侧和被引用侧都是如此。

这也解释了选择查询的工作原理。

【讨论】：