How to make SQL query that will combine rows of result from one table with rows of another table in specific conditions in SQLite - sql

Question

I have aSQLite3 database with three tables. Sample data looks like this:
Original
id aName code
------------------
1 dog DG
2 cat CT
3 bat BT
4 badger BDGR
... ... ...
Translated
id orgID isTranslated langID aName
----------------------------------------------
1 2 1 3 katze
2 1 1 3 hund
3 3 0 3 (NULL)
4 4 1 3 dachs
... ... ... ... ...
Lang
id Langcode
-----------
1 FR
2 CZ
3 DE
4 RU
... ...
I want to select all data from Original and Translated in way that result would consist of all data in Original table, but aName of rows that got translation would be replaced with aName from Translated table, so then I could apply an ORDER BY clause and sort data in the desired way.
All data and table designs are examples just to show the problem. The schema does contain some elements like an isTranslated column or translation and original names in separate tables. These elements are required by application destination/design.
To be more specific this is an example rowset I would like to produce. It's all the data from table Original modified by data from Translated if translation is available for that certain id from Original.
Desired Result
id aName code isTranslated
---------------------------------
1 hund DG 1
2 katze CT 1
3 bat BT 0
4 dachs BDGR 1
... ... ... ...

Answer 1

This is a typcial application for the CASE expression:
SELECT Original.id,
CASE isTranslated
WHEN 1 THEN Translated.aName
ELSE Original.aName
END AS aName,
code,
isTranslated
FROM Original
JOIN Translated ON Original.id = Translated.orgID
WHERE Translated.langID = (SELECT id FROM Lang WHERE Langcode = 'DE')
If not all records in Original have a corresponding record in Translated, use LEFT JOIN instead.
If untranslated names are guaranteed to be NULL, you can just use IFNULL(Translated.aName, Original.aName) instead.

Answer 2

You should probably list the actual results you want, which would help people help you in the future.
In the current case, I'm guessing you want something along these lines:
SELECT Original.id, Original.code, Translated.aName
FROM Original
JOIN Lang
ON Lang.langCode = 'DE'
JOIN Translated
ON Translated.orgId = Original.id
AND Translated.langId = Lang.id
AND Translated.aName IS NOT NULL;
(Check out my example to see if these are the results you want).
In any case, the table set you've got is heading towards a fairly standard 'translation table' setup. However, there are some basic changes I'd make.
Original
Name the table to something specific, like Animal
Don't include a 'default' translation in the table (you can use a view, if necessary).
'code' is fine, although in the case of animals, genus/species probably ought to be used
Lang
'Lanugage' is often a reserved word in RDBMSs, so the name is fine.
Specifically name which 'language code' you're using (and don't abbreviate column names). There's actually (up to) three different ISO codes possible - just grab them all.
(Also, remember that languages have language-specific names, so language also needs it's own 'translation' table)
Translated
Name the table entity-specific, like AnimalNameTranslated, or somesuch.
isTranslated is unnecessary - you can derive it from the existence of the row - don't add a row if the term isn't translated yet.
Put all 'translations' into the table, including the 'default' one. This means all your terms are in one place, so you don't have to go looking elsewhere.