MaridDB 10.3.29 prevents me from deleting a foreign key

Question

This is a minimal example that triggers the error

CREATE TABLE A (
  id bigint NOT NULL AUTO_INCREMENT PRIMARY KEY
);

CREATE TABLE B (
  what tinyint NOT NULL,

  a bigint NOT NULL,

  CONSTRAINT x FOREIGN KEY (a) REFERENCES A(id),
  CONSTRAINT y CHECK (what > 0)
);


SELECT b.a FROM B b;

ALTER TABLE B DROP CONSTRAINT x;

When i run this in a fresh MariaDB instance (docker mariadb:10.3.28) everything works fine.

When MariaDB 10.3.29 was released the query suddenly broke. So, when i run this in a fresh MariaDB instance (docker mariadb:10.3.29) i get the following error message for the last statement:

[42S22][1054] (conn=8) Unknown column '`db`.`b`.`what`' in 'CHECK'

Some weird observations:

• if i delete the y check and add it after dropping x everything works
• if i remove the SELECT everything works
• the b from the error message changes with the table alias from the SELECT statement
• running the last statement again shows the same error
• the error message makes no sense at all

So my question: what's wrong with my SQL?

Answer 1

This is actually a bug in MariaDB. See the bugtracker.

They recommended to do FLUSH TABLES; before the ALTER statement.

I can confirm that this "hides the bug".