learning about calibre-debug

I'm trying to run some batch jobs using python and calibre-debug -c

command = (
f"from calibre.library.database2 import LibraryDatabase2; "
f"db = LibraryDatabase2('/Calibre/'); "
f"db.conn.execute('UPDATE books_languages_link SET lang_code={lang_id} WHERE book={book_id}'); "
f"db.conn.execute('UPDATE custom_column_4 SET value=1 WHERE book={book_id}'); "
f"db.conn.commit();"

I suppose that this does not do anything if there is not already a language populated nor a custom_column_4 entry made for this particular book (like an upsert).

Is there a more intelligent way to do this that directly checks if this needs updating or inserting via calibre-debug? I've seen some nice ones in this forum.. but I don't understand the syntax

is there a sort of guide on how to construct these statements properly?

many thanks for your help!