Getting the "latest" related record from a SQL DB
estrai at estrai.com
Thu Oct 9 20:55:02 BST 2014
Storing that data in a separate table might make sense if it will be accessed often.
However I would suggest a subselect if the above is not the case, technically these are two queries yes, but it’s up to the database to optimize them.
test=# select * from artist;
id | name
1 | Prince
2 | Björk
test=# select * from album;
id | artist_id | name
1 | 1 | 20Ten
2 | 1 | Art Official Age
3 | 1 | PLECTRUMELECTRUM
4 | 2 | Drawing Restraint 9
5 | 2 | Anna and the Moods
6 | 2 | Björk: Biophilia Live
test=# select artist.name, album.name from album join artist on (artist.id = album.artist_id) where album.id = (select max(id) from album where album.artist_id = artist.id);
name | name
Prince | PLECTRUMELECTRUM
Björk | Björk: Biophilia Live
On 9 Oct 2014, at 13:28, Andrew Beverley <andy at andybev.com> wrote:
> Hi guys,
> I'm after some best-practice advice regarding SQL database design.
> I have a table (say "artist", couldn't resist...) that has a one-to-many
> relationship to another table (say "album"). The album table has a field
> which references the artist table's ID. So one artist can have many
> So, if I want to know all of an artist's albums, that's easy.
> But what if I want to fetch an artist's details and his latest album? I
> can select the artist from the artists table and then join the albums
> table. But to get the latest album I'd have to use a max function (say
> on the album's date), with which it isn't possible to get the related
> fields in the same row.
> I see 2 ways of solving this:
> - Run multiple queries to get the relevant album's ID (if even possible)
> and then retrieve its row in entirety.
> - Have a reference from the artist table back to the album table,
> specifying which is the latest album, which I update each time the
> albums table is updated.
> Neither seem particularly tidy to me, so am I missing something
> completely obvious?
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