Refactor foreign key to fields

Question

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 relatio

Answer 1

Your seem to go the wrong way. Your original, normalized schema is typically superior. If you need to display shop / user, create a VIEW.

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;

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.

About varchar(255):

• Should I add an arbitrary length limit to VARCHAR columns?
• Any downsides of using data type "text" for storing strings?
• More details in the manual.