Is the index related to predicate, or are they independent entitites?

Question

It is a theoretical question I can't seem to get my head around. Is the index related to the predicate, and if yes, how? Thanks in advance!

Answer 1

Predicates are an Ed Codd, relational ideal.

Indexes have more to do with the physical implementation of the table. They help make searches faster (e.g. B-tree representation).

Predicates can be mapped to WHERE clauses and indexes in actual implementations, but I think predicate is more abstract and theoretical. It doesn't know or care about how you decide to implement the relation. Predicate is still true whether you do a TABLE SCAN or index it properly.