multi-part vector indexes

The idea is to allow indexes like

CREATE TABLE notes (

  note_id INT PRIMARY KEY,

  author_id INT,

  embed VECTOR(1024),

  VECTOR INDEX (author_id, embed)

)

which will essentially create distinct vector graphs per author_id. Naturally, it will only support vector searches for queries like

SELECT note_id FROM notes WHERE author_id=1234 ORDER by VEC_DISTANCE_COSINE(embed, x'...') LIMIT 5

Using one graph for all authors will be much slower, if the selectivity of the WHERE clause is high, because the search will need to produce many candidate vectors that will be ultimately rejected by WHERE