Select fields and filter rows from structured records

You get a schema (a list of field names) and records whose values line up with it. Implement a tiny query: given the fields to return and a list of equality filters (field and expected value), return the selected fields of every record that passes all filters, in record order and in the requested field order.

If any requested or filtered field is not in the schema, the whole query is invalid. No filters means every record matches. Think about how you map names to positions once rather than per record.