Sqlite

Sqlite has support for virtual tables which can be used for external datasources. There is an example csv data source that allows you to query a csv file as if it was a regular table.

.load ./csv
CREATE VIRTUAL TABLE temp.csv USING csv(filename=FILENAME);
SELECT * FROM csv;

I do not really want to write C for this, but I found the rusqlite project which allows writing a loadable_extension that provides virtual tables. Using their vtablog example (slightly modified) I was able to test from sqlite with a rust module.