In a lot of ways the Logic Programming languages are effectively relational (e.g. Prolog, Datalog, KIF) but the search behavior for relations that satisfy a query is a bit different than SQL-like relational languages.
On a previous project I embedded a SQL-like sub-language into a model language so that ETL pipelines and OLAP/OLTP processing could be generated to query aggregates and value lookups during inference. It is nontrivial to embed a relational language into another language without making some compromises but there are certainly contexts where it is quite useful. I think C#'s LINQ is a reasonable effort at this but I'm not much a fan of the rest of that language.
On a previous project I embedded a SQL-like sub-language into a model language so that ETL pipelines and OLAP/OLTP processing could be generated to query aggregates and value lookups during inference. It is nontrivial to embed a relational language into another language without making some compromises but there are certainly contexts where it is quite useful. I think C#'s LINQ is a reasonable effort at this but I'm not much a fan of the rest of that language.