Language fallback with database content in OpenCart - sql

Question

I've just (6 months+) started learning all the web languages, mostly within OpenCart's framework. Right now I'm trying to get language fallback to work with database content.
The objective is to check for an empty field in id.title and if so choose the default language_id=1.
The language_id comes from a GET request invoked by the frontend user.
The table description looks like this:
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| information_id | language_id | title | description |
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| 3 | 1 | policy | policy desc |
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| 4 | 1 | about | about desc |
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| 4 | 2 | | |
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| 5 | 1 | terms | terms desc |
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| 6 | 1 | comp | comp desc |
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As you can see language_id=2 has no title nor description (inserted by sql, not oc's admin). In this case I want to get the row with the default language=1.
I've tried using CASE but the results are always empty. The problem I can't find a solution for this is to check the title field next to the requested language_id.
I've also tried to first check the field before doing a SELECT, but no success.
SELECT DISTINCT *
FROM information_description id
WHERE id.information_id = '4'
AND id.language_id = (CASE WHEN id.title = '' THEN '1' ELSE '2' END);
Any help would be appreciated.

Answer 1

Here You have two options. Either do this by subselects or once per save/update walk through all the information descriptions and update the missing languages with the texts from the default ones.
The first solution could be:
SELECT id.information_id, id.language_id, id.description,
CASE WHEN id.title IS NOT NULL /* or CASE WHEN id.title <> '' - depending on the real value in DB when it's empty */
THEN id.title
ELSE (SELECT title FROM information_description WHERE language_id = 1)
AS title
FROM information_description id
WHERE id.language_id = 2
I would call such query only in the case when the language ID differs from the default one. Since this may look like working solution I don't like it simply because it increases the DB effort.
Instead of this I recommend to simply update Your missing data in similar way (this could be done maybe only once per life and you are done):
UPDATE information_description id SET
id.title = (SELECT title FROM information_description WHERE language_id = 1 AND information_id = id.information_id)
WHERE id.language_id <> 1
AND id.title IS NULL
for title and
UPDATE information_description id SET
id.description = (SELECT description FROM information_description WHERE language_id = 1 AND information_id = id.information_id)
WHERE id.language_id <> 1
AND id.description IS NULL
for description fields...