SQLite full-text search relevance ranking

For FTS5, according to SQLite FTS5 Extension,

• FTS5 has no matchinfo().
• FTS5 supports ORDER BY rank

So very simply, something like

SELECT * FROM email WHERE email MATCH 'fts5' ORDER BY rank;

without DESC works.

There's a complete example in the documentation, look at the end of appendix a. You'll need to do slightly more work to get a good relevance ranking as the function provided is good only for getting started. For example, with matchinfo(table,'pcnalx') there's enough information to implement Okapi BM25.

There seems to be a distinct lack of documentation on how to implement Okapi BM25 in C and it seems it is an unspoken thing that the implementation is left as an exercise for the user.

Well I found the bro of a programmer "Radford 'rads' Smith" who chucked this up on GitHub

https://github.com/rads/sqlite-okapi-bm25

It only implements BM25 although I'm looking into BM25F tweaks now....

....and here it is.

https://github.com/neozenith/sqlite-okapi-bm25