CREATE TABLE t2 (id INTEGER PRIMARY KEY, j VARCHAR UNIQUE);
SELECT 
	column_name,
	data_type AS "column_type",
	CASE WHEN is_nullable THEN 'YES' ELSE 'NO' END AS "null",
	(
		SELECT MIN(
			CASE WHEN constraint_type='PRIMARY KEY' THEN 'PRI'
			WHEN constraint_type='UNIQUE' THEN 'UNI'
			ELSE NULL END)
		FROM duckdb_constraints() c
		WHERE c.table_oid=cols.table_oid AND list_contains(constraint_column_names, cols.column_name)
	) AS "key",
	column_default AS "default",
	NULL AS "extra"
FROM duckdb_columns cols WHERE table_name='t2';
┌─────────────┬─────────────┬─────────┬─────────┬─────────┬───────┐
│ column_name │ column_type │  null   │   key   │ default │ extra │
│   varchar   │   varchar   │ varchar │ varchar │ varchar │ int32 │
├─────────────┼─────────────┼─────────┼─────────┼─────────┼───────┤
│ id          │ INTEGER     │ NO      │ PRI     │ NULL    │  NULL │
│ j           │ VARCHAR     │ YES     │ UNI     │ NULL    │  NULL │
└─────────────┴─────────────┴─────────┴─────────┴─────────┴───────┘