Enable relationship matching based on more than one column

Problem/Motivation

In the case of a base file with columns for country and year, and a relationship file with the same columns, users often need to match on both columns to ensure data accuracy. To do this, we need to create a composite key.

Steps to reproduce

Create a Base CSV with columns: Country, Year, ID.

Row 1: Ghana, 2024, 1

Create a Relationship CSV with columns: Country, Year, Value.

Row 1: Ghana, 2024, A

Row 2: Ghana, 2025, B

Create a View based on the Base CSV.

Add a Relationship to the second CSV, joining on both Country.

Result: The View displays 2 rows for Ghana 2024.

Expected Result: 1 row (Ghana 2025).