将外键重构为字段 [英] Refactor foreign key to fields
问题描述
在 PostgreSQL 中我需要重构一个表 (Purchases);它有另一个表的外键(Shop).相反，我想要两个以文本方式保持关系的字段.我不能丢失任何信息，表格已经包含数据.
In PostgreSQL I need to refactor a table (Purchases); it has a foreign key to another table (Shop). Instead I want two fields that keep the relation in a textual way. I must NOT lose any information, the tables already contain data.
Purchases.shop_id: (long) -- is the field I need to drop
Purchases.shop: (characters) -- will hold the Shop's name
Purchases.shop_user: (characters) -- will hold the Shop's user name.
Shop.id: (long, pk) -- still referenced from Purchases
Shop.name: (characters) -- Shop's name
Shop.user: (characters) -- Shop's user name
两个字段是必需的，因为 Shop 在 (name,user) 上是唯一的(当然也可以是 id).
Two fields are necessary because a Shop is unique on (name,user) (or by id of course).
ALTER TABLE Purchases ADD COLUMN shop CHARACTER VARYING(255);
ALTER TABLE Purchases ADD COLUMN shop_user CHARACTER VARYING(255);
-- ???
ALTER TABLE Purchases DROP CONSTRAINT shop_id_fk;
ALTER TABLE Purchases DROP COLUMN shop_id;
所以开头和结尾很简单，有人可以帮忙做中间部分吗?:)
So the start and the ending is easy, can somebody help with middle-part? :)
我知道外键是为此而设计的，但我必须这样做.
I know that foreign keys were made for this but I have to do it this way.
推荐答案
你好像走错路了.您的原始规范化模式通常更优越.如果需要显示店铺/用户，创建一个VIEW.
Your seem to go the wrong way. Your original, normalized schema is typically superior. If you need to display shop / user, create a VIEW.
但你可能有你的理由，所以这里是:
But you may have your reasons, so here goes:
UPDATE purchases p
SET (shop, shop_user) = (s.name, s."user")
FROM shop s
WHERE s.id = p.shop_id;
不要使用 保留字 用户" 作为标识符.
和名字"名字也不是一个好名字.
而 Postgres 中的 varchar(255) 通常表示误解.
Don't use the reserved word "user" as identifier.
And "name" is hardly ever a good name, either.
And varchar(255) in Postgres typically indicates a misunderstanding.
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