FOREIGN KEY clause in CREATE TABLE ... ENGINE=DuckDB is silently accepted without any error or warning

INSTALL SONAME 'ha_duckdb';

CREATE TABLE parent (id INT PRIMARY KEY) ENGINE=DuckDB;

CREATE TABLE child (id INT PRIMARY KEY, parent_id INT, FOREIGN KEY (parent_id) REFERENCES parent(id)) ENGINE=DuckDB;

SHOW CREATE TABLE child;

SHOW WARNINGS;

INSERT INTO child VALUES (1, 999);

SELECT * FROM child;

13.1.0-dbg>INSTALL SONAME 'ha_duckdb';

Query OK, 0 rows affected (1.023 sec)

13.1.0-dbg>CREATE TABLE parent (id INT PRIMARY KEY) ENGINE=DuckDB;

Query OK, 0 rows affected (0.030 sec)

13.1.0-dbg>CREATE TABLE child (id INT PRIMARY KEY, parent_id INT, FOREIGN KEY (parent_id) REFERENCES parent(id)) ENGINE=DuckDB;

Query OK, 0 rows affected (0.022 sec)

13.1.0-dbg>SHOW CREATE TABLE child;

+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

| Table | Create Table                                                                                                                                                                                                    |

+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

| child | CREATE TABLE `child` (

  `id` int(11) NOT NULL,

  `parent_id` int(11) DEFAULT NULL,

  PRIMARY KEY (`id`),

  KEY `parent_id` (`parent_id`)

) ENGINE=DUCKDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_uca1400_ai_ci |

+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

1 row in set (0.000 sec)

13.1.0-dbg>SHOW WARNINGS;

Empty set (0.000 sec)

13.1.0-dbg>INSERT INTO child VALUES (1, 999);

Query OK, 1 row affected (0.044 sec)

13.1.0-dbg>SELECT * FROM child;

+----+-----------+

| id | parent_id |

+----+-----------+

|  1 |       999 |

+----+-----------+

1 row in set (0.034 sec)

13.1.0-dbg>