11.5.0-dbg>CREATE TABLE t (c1 INT PRIMARY KEY,c2 INT,FOREIGN KEY(c2) REFERENCES t (c1));

Query OK, 0 rows affected (0.011 sec)

11.5.0-dbg>ALTER TABLE t DROP PRIMARY KEY;

ERROR 1025 (HY000): Error on rename of './test/#sql-alter-2ff04a-4' to './test/t' (errno: 150 "Foreign key constraint is incorrectly formed")

11.5.0-dbg>SHOW WARNINGS;                          

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

| Level | Code | Message                                                                                                                   |

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

| Error | 1025 | Error on rename of './test/#sql-alter-2ff04a-4' to './test/t' (errno: 150 "Foreign key constraint is incorrectly formed") |

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

1 row in set (0.000 sec)

2024-06-15 11:50:06 4 [ERROR] InnoDB: In ALTER TABLE `test`.`t` has or is referenced in foreign key constraints which are not compatible with the new table definition.

--source include/have_innodb.inc

CREATE TABLE t (c1 INT PRIMARY KEY,c2 INT,FOREIGN KEY(c2) REFERENCES t (c1)) ENGINE=InnoDB;

ALTER TABLE t DROP PRIMARY KEY;

SHOW WARNINGS;