ALTER IGNORE ... ADD FOREIGN KEY ... ALGORITHM=COPY causes bogus ER_TABLE_EXISTS_ERROR and lengthy InnoDB error message

--source include/have_innodb.inc

CREATE TABLE t1 (f1 INT, f2 INT, f3 INT, KEY(f1)) ENGINE=InnoDB;

CREATE TABLE t2 (f INT, KEY(f)) ENGINE=InnoDB;

ALTER TABLE t1 ADD FOREIGN KEY (f2) REFERENCES t2 (f);

ALTER IGNORE TABLE t1 ADD FOREIGN KEY (f3) REFERENCES t1 (f1), ALGORITHM=COPY;

# Cleanup

DROP TABLE t1, t2;

CURRENT_TEST: bug.t5a

mysqltest: At line 7: query 'ALTER IGNORE TABLE t1 ADD FOREIGN KEY (f3) REFERENCES t1 (f1), ALGORITHM=COPY' failed: 1050: Table './test/t1' already exists

2019-01-05 00:14:36 7f391882c700  InnoDB: Error; possible reasons:

InnoDB: 1) Table rename would cause two FOREIGN KEY constraints

InnoDB: to have the same internal name in case-insensitive comparison.

InnoDB: 2) table `test`.`t1` exists in the InnoDB internal data

InnoDB: dictionary though MySQL is trying to rename table `test`.`#sql-5a68_3` to it.

InnoDB: Have you deleted the .frm file and not used DROP TABLE?

InnoDB: You can look for further help from

InnoDB: http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html

InnoDB: If table `test`.`t1` is a temporary table #sql..., then it can be that

InnoDB: there are still queries running on the table, and it will be

InnoDB: dropped automatically when the queries end.

InnoDB: You can drop the orphaned table inside InnoDB by

InnoDB: creating an InnoDB table with the same name in another

InnoDB: database and copying the .frm file to the current database.

InnoDB: Then MySQL thinks the table exists, and DROP TABLE will

InnoDB: succeed.