```json { "classifications": [ { "column": "reading_id", "label": "primary_key", "confidence": 1.0, "reason": "100% distinct (580/580), zero nulls, prefixed 'mr_' suggests unique identifier for metric readings" }, { "column": "metric_id", "label": "foreign_key", "confidence": 1.0, "reason": "Only 2 distinct values in 580 rows, prefixed 'm_' suggests reference to metrics table" }, { "column": "period_start", "label": "none", "confidence": 1.0, "reason": "24 distinct date values, represents time dimension, not a key" }, { "column": "segment", "label": "none", "confidence": 1.0, "reason": "28 distinct values including empty string, categorical dimension for segmentation" }, { "column": "numerator", "label": "none", "confidence": 1.0, "reason": "98 distinct numeric values, metric component, not a key" }, { "column": "denominator", "label": "none", "confidence": 1.0, "reason": "248 distinct numeric values, metric component, not a key" }, { "column": "n", "label": "none", "confidence": 1.0, "reason": "248 distinct count values, appears to be sample size, not a key" }, { "column": "value", "label": "none", "confidence": 1.0, "reason": "321 distinct computed values (0.0-1.0), metric result, not a key" }, { "column": "computed_at", "label": "none", "confidence": 1.0, "reason": "Only 2 distinct timestamps, represents computation time, not a key" }, { "column": "batch_id", "label": "foreign_key", "confidence": 0.95, "reason": "Single batch value for all rows, prefixed 'batch_' suggests reference to batch processing table" }, { "column": "sql_fingerprint", "label": "none", "confidence": 1.0, "reason": "2 distinct hash values, identifies SQL query used, not a relational key" } ] } ```