Support for the sparse embeddings

[magaton]

The latest pgvector version supports sparsevec.
However, langchain's PGVector supports only one embeddings column in langchain_pg_embedding table.
It would be great to have a sparse_embedding column and sparse_embedding field in PGVector.

I have considered the alternative and that is to have 2 PGVector stores, 1 for dense and 1 for sparse vectors. However there are 2 problems with that:

• PGVector has hardcoded table names for collection and embeddings
• I would like to leverage excellent langchain indexer with SQL manager.

[gecBurton]

hi @magaton I would be interested in collaborating on this, I would also like some kind of full-text/dense feature #61

[Freezaa9]

Hello, would be interested also.

But I think each vector DB should be separated.
So for a hybrid search it would be

• One Dense embedding vector DB (using the current feature)
• One Sparse Vector DB (using https://github.com/pgvector/pgvector-python/blob/master/examples/hybrid_search/cross_encoder.py)

And then rerank by using EnsembleRetriever (for example: https://python.langchain.com/docs/how_to/ensemble_retriever/ )

To achieve this we should also bump the pgvector python version: #82

[gecBurton]

hi, I could really do with this feature. I have made a very crude PR that suggests how this might be done, I would appreciate some help as I do not know this codebase well :) #204