How to search for compound words, and get the word parts returned
I would look for a library that specializes in splitting compound words.  Search Java, PHP, Perl, etc.  SQL is not likely to be involved.

If you must use a database, then consider this for a piece of the algorithm:

SELECT word FROM words
    WHERE word &lt; 'menneskerettighedsforkæmperens'
    ORDER BY word DESC
    LIMIT 5;


That is likely to return a few compound words that begin with 'menneske' and perhaps 'menneske', itself.

In MySQL, that query will be quite fast (assuming an index on word).  You would need some code in addition to a few SQL calls.