SQLite Select first row per category - sql

Question

I'm trying to write a mutli-language blog software using Python and sqlite and I'm struggeling with making an sql query elegant.
I've got all articles of the blog in two tables:
articleindex (contains most of the metadata of the articles like the URL, etc)
articlecontent (contains well, the content of the article, and a flag for the language, and when this specific translation was written (aka, the date))
I now try to select all articles ordered by date and by language. This if for the main view of the blog. It should list all articles in chronological order, regardless of the language they are in, but only once (I don't want to have the english version of an article below or above the german version) - if there are multiple translations the main view should contain the default language (english) if it exists. If there is no english version it should show the german version (if it exits) if there is no german version it shall show the esperanto version, etc.
Of course I can do this in python, select all articles, and skip a record if the another version of the article has already been written. However this seemed inelegant. I'd rather liked SQLite to return the data as need.
So far I could manage to get the data in the order I want, I just don't seem to be able to eliminate the unneeded records.
Here is the table structure:
CREATE TABLE articleindex (id INTEGER PRIMARY KEY,
category text,
translationid text,
webid text) `
CREATE TABLE articlecontent (id INTEGER PRIMARY KEY,
articleindexid INTEGER,
lang text,
content text,
date text) `
I came up with this query, which gives me the right order, but has duplicates in it:
SELECT * FROM articlecontent AS ac LEFT JOIN articleindex AS ai
ON ac.articleindexid = ai.id ORDER BY ac.date DESC, CASE ac.lang
WHEN "en" THEN 0
WHEN "de" THEN 1
WHEN "eo" THEN 2
END
This results in the (shortend) output:
articleindexid. lang
21, en
21, de
12, en
12, de
8, en
8, de
2, en
2, de
2, eo
How do I skip for example the second record with the articleindexid 21 or 12?
Using search engines I came across suggestions about using Partitions, but it seems Sqlite doesn't support those. I also have difficulties for what to search for, so any suggestion is appreciated.
Thanks
Ben

Answer 1

I think you should create table for language priorities to use it instead of CASE in SQL statemens. For example
LANG_PRIORITY(lang text,Ord INTEGER) = (("en",0),("de",1),("eo",2))
Anyway in your current environment try to use the following query. The subquery with LIMIT 1 will select one row per DATE with higher priority:
SELECT * FROM articlecontent AS ac
LEFT JOIN articleindex AS ai
ON ac.articleindexid = ai.id
WHERE ac.id =
(
SELECT ID FROM articlecontent as ac2
WHERE ac.date=ac2.date
ORDER BY CASE ac2.lang
WHEN "en" THEN 0
WHEN "de" THEN 1
WHEN "eo" THEN 2
END
LIMIT 1
)
ORDER BY ac.date DESC