Mysql query with group by having

Question

I have a table with 3 columns: id, sentence and language. So sentences can be either in English and German, IDs are assigned to sentences with same meaning but different languages, like

ID | sentence | language
1  | Hello    | en
1  | Hallo    | de
2  | Sorry    | en

there could be sentences that exist only in one language. Now I want to find out all sentences that are available in both language, I can do with:

SELECT 
    *
FROM
    `sentences`
WHERE
    LENGTH(sentence) > 0
        AND (language = 'en' OR language = 'de')
GROUP BY id
HAVING COUNT(language) = 2

and I get results of sentences only in German. Then I do

SELECT 
    *
FROM
    sentences
WHERE
    id IN (SELECT 
            id
        FROM
            `sentences`
        WHERE
            LENGTH(sentence) > 0
                AND (language = 'en' OR language = 'de')
        GROUP BY id
        HAVING COUNT(language) = 2)

That should work but query takes forever. My question: is there any fancy way to do this?

Answer 1

INNER JOINS are faster than using IN clause

SELECT en.id, 
       en.sentence as en_sentence,
       de.sentence as de_sentence,
       en.language as en_language,
       de.language as de_language
FROM sentences en
INNER JOIN sentences de ON en.ID = de.ID AND en.language = 'en' AND de.language = 'de'
WHERE length(en.sentence) > 0
AND length(de.sentence) > 0