{"abstract":"Repeated tuples containing an unknown component are rejected as duplicate composite keys.","category":"Storage and queries","checks":7,"contract":"Return whether a list of two-component keys satisfies ordinary NULL-distinct SQL UNIQUE semantics: two rows conflict only when both components in both rows are non-NULL and equal. None represents SQL NULL.","contract_signature":"rows","evaluation_group":"xs-composite-index-conflicts","failed_approach":"Exempting only a NULL in the first column still treats a NULL in the second column as an equal comparable value.","family":"store-nullable-composite-unique","id":"FA-131","implementations":{"attempt":{"sha256":"84c1b6d242630d1df6c56e5f70497b1128e7d3328dcc66f07878480fb816a966","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(rows):\n    comparable = [tuple(row) for row in rows if row[0] is not None]\n    return len(set(comparable)) == len(comparable)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('unknown second component can repeat', solve([[N, None], [N, None]]), True)\ncheck('unknown first component can repeat', solve([[None, N], [None, N]]), True)\ncheck('both components unknown can repeat', solve([[None, None]] * (N+1)), True)\ncheck('fully known repeated key conflicts', solve([[N, N+1], [N, N+1]]), False)\ncheck('known zero is not unknown', solve([[N, 0], [N, 0], [None, 0]]), False)\ncheck('different complete tuples coexist', solve([[N, N+1], [N, N+2], [N+1, N+1]]), True)\ncheck('empty relation satisfies uniqueness', solve([]), True)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"6db7713cbba3e546dfc5ae29cb02eaed0d786da4e5e8a88aa619e37fca0c2125","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(rows):\n    return len(set(map(tuple, rows))) == len(rows)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('unknown second component can repeat', solve([[N, None], [N, None]]), True)\ncheck('unknown first component can repeat', solve([[None, N], [None, N]]), True)\ncheck('both components unknown can repeat', solve([[None, None]] * (N+1)), True)\ncheck('fully known repeated key conflicts', solve([[N, N+1], [N, N+1]]), False)\ncheck('known zero is not unknown', solve([[N, 0], [N, 0], [None, 0]]), False)\ncheck('different complete tuples coexist', solve([[N, N+1], [N, N+2], [N+1, N+1]]), True)\ncheck('empty relation satisfies uniqueness', solve([]), True)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":" This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"store-nullable-composite-unique","generated_at":"2026-09-29T14:36:50.519359+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Isolates a storage constraint's comparison contract. Some engines offer NULLS NOT DISTINCT constraints; that alternate contract is explicitly outside this experiment, so the model does not label it a database bug.","root_cause":"Python tuple equality is used for a SQL UNIQUE contract under which a NULL in any component prevents equality conflicts.","sha256":"b09f31b7291d2af5137f560d1f5211cfdc9c6c07890b25e7aa48718cce73e973","title":"A composite uniqueness check rejects SQL-valid nullable keys · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":36.072,"exit_code":1,"observations":[{"actual":false,"check":"unknown second component can repeat","expected":true,"passed":false},{"actual":true,"check":"unknown first component can repeat","expected":true,"passed":true},{"actual":true,"check":"both components unknown can repeat","expected":true,"passed":true},{"actual":false,"check":"fully known repeated key conflicts","expected":false,"passed":true},{"actual":false,"check":"known zero is not unknown","expected":false,"passed":true},{"actual":true,"check":"different complete tuples coexist","expected":true,"passed":true},{"actual":true,"check":"empty relation satisfies uniqueness","expected":true,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"unknown second component can repeat\", \"actual\": false, \"expected\": true, \"passed\": false}, {\"check\": \"unknown first component can repeat\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"both components unknown can repeat\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"fully known repeated key conflicts\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"known zero is not unknown\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"different complete tuples coexist\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"empty relation satisfies uniqueness\", \"actual\": true, \"expected\": true, \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":33.852,"exit_code":1,"observations":[{"actual":false,"check":"unknown second component can repeat","expected":true,"passed":false},{"actual":false,"check":"unknown first component can repeat","expected":true,"passed":false},{"actual":false,"check":"both components unknown can repeat","expected":true,"passed":false},{"actual":false,"check":"fully known repeated key conflicts","expected":false,"passed":true},{"actual":false,"check":"known zero is not unknown","expected":false,"passed":true},{"actual":true,"check":"different complete tuples coexist","expected":true,"passed":true},{"actual":true,"check":"empty relation satisfies uniqueness","expected":true,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"unknown second component can repeat\", \"actual\": false, \"expected\": true, \"passed\": false}, {\"check\": \"unknown first component can repeat\", \"actual\": false, \"expected\": true, \"passed\": false}, {\"check\": \"both components unknown can repeat\", \"actual\": false, \"expected\": true, \"passed\": false}, {\"check\": \"fully known repeated key conflicts\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"known zero is not unknown\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"different complete tuples coexist\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"empty relation satisfies uniqueness\", \"actual\": true, \"expected\": true, \"passed\": true}], \"passed\": false}\n"}},"member_only":{"stages":["fixed"],"fields":["implementations.fixed","verification.fixed","harness","repair"],"note":"The verified repair, its recorded checks, the repair description, and the scoring harness are available to members."}}