zkuste něco takového:
SELECT
e.key,COALESCE(o.value,e.value)
FROM Translation e
LEFT OUTER JOIN Translation o ON e.key=o.key and o.language_code='nl'
WHERE e.language_code='en'
zkuste něco takového:
SELECT
e.key,COALESCE(o.value,e.value)
FROM Translation e
LEFT OUTER JOIN Translation o ON e.key=o.key and o.language_code='nl'
WHERE e.language_code='en'