Codd's seminal paper, A Relational Model of Data for Large Shared Data Banks, states that a language based on applied predicate calculus "would provide a yard-stick of linguistic power for all other proposed data languages". Quoting from https://www.seas.upenn.edu/~zives/03f/cis550/codd.pdf:

"1.5 Some linguistic aspects

The adoption of a relational model of data, as described above, permits the development of a universal data sub-language based on an applied predicate calculus. A first-order predicate calculus suffices if the collection of relations is in normal form. Such a language would provide a yard-stick of linguistic power for all other proposed data languages, and would itself be a strong candidate for embedding (with appropriate syntactic modification) in a variety of host languages (programming, command- or problem-oriented)."

Languages based on predicate calculus indeed seem extremely suitable for reasoning about relational data. Datalog is a well-known example. It is more directly based on predicate logic, and much simpler than SQL.