PostgreSQL 从另一个表更新一个表，连接成多对多

Question

I have three tables: user , image and user_images_image (cos the first two related as ManyToMany). I would like to set the profile_pic of the user table to the value of the name property taken from the image table.

I know how to build a SELECT query for something like this but it's not very helpful... I would write something like this:

SELECT "user".id, image.name FROM "user"
LEFT JOIN user_images_image uii ON "user".id = uii."userId"
LEFT JOIN image ON uii."imageId" = image."id"
WHERE "user".id = 2;

In PostgreSQL I can't just join two tables the way I would in MySQL.

How do I write such a query?

Answer 1

In Postgres, you would use the update/join syntax as follows:

update "user" u
set profile_pic = i.name
from user_images_image uii
inner join image i on uii."imageId" = i."id"
where uii."userId" = u.id and u.id = ? and i.id = ?

If there are no missing images, then an alternative is a correlated subquery:

update "user" u
set profile_pic = (
    select i.name
    from user_images_image uii
    inner join image i on uii."imageId" = i."id"
    where uii."userId" = u.id and i.id = ?
) 
where u.id = ?