```json { "table_name": "2019", "primary_key": "Country or region", "candidates": [ { "rank": 0, "partition_key": "Country or region", "partition_key_label": "primary_identifier", "partition_key_reasoning": "RPUV=1.00, uniqueness=1.000, 0% null. Each country appears exactly once in this 2019 snapshot. Semantically the natural identifier for a dimension table of country happiness metrics.", "clustering_key": null, "clustering_key_label": null, "clustering_key_reasoning": "Dimension tables typically do not require internal sorting. All rows are independent country records.", "world_line": null, "session_column": null, "confidence": "HIGH", "notes": "This is a single-year (2019) snapshot dimension table. The presence of sibling tables (2015, 2016, 2017, 2018) suggests this dataset contains one table per year. Country or region is the unique identifier. Overall rank is also unique but is a derived metric, not a stable identifier." } ] } ```