INPLACE DROP COLUMN error reports internal foreign-key identifier instead of constraint name

When an INPLACE ALTER TABLE ... DROP COLUMN is rejected because the column is referenced by a foreign key, error 1829 reports an internal database/table identifier instead of the SQL-visible constraint name. The statement-local foreign_key_checks=0 override is required to reach this diagnostic path and does not change the global setting.

Steps to reproduce

1. Save the following as setup.sql:

CREATE DATABASE diag;

USE diag;

CREATE TABLE parent (

  id INT PRIMARY KEY, ref INT UNIQUE

) ENGINE=InnoDB;

CREATE TABLE child (

  id INT PRIMARY KEY, ref INT,

  CONSTRAINT fk_ref FOREIGN KEY (ref)

    REFERENCES parent(ref)

) ENGINE=InnoDB;

2. Save the COPY operation as copy.sql:

USE diag;

SET STATEMENT foreign_key_checks=0 FOR

ALTER TABLE parent DROP COLUMN ref, ALGORITHM=COPY;

3. Save the equivalent INPLACE operation as inplace.sql:

USE diag;

SET STATEMENT foreign_key_checks=0 FOR

ALTER TABLE parent DROP COLUMN ref, ALGORITHM=INPLACE;

4. Save the metadata check as metadata.sql:

SELECT TABLE_NAME, COLUMN_NAME FROM information_schema.COLUMNS

WHERE TABLE_SCHEMA='diag'

ORDER BY TABLE_NAME, ORDINAL_POSITION;

SELECT TABLE_NAME, CONSTRAINT_NAME FROM information_schema.REFERENTIAL_CONSTRAINTS

WHERE CONSTRAINT_SCHEMA='diag';

5. Run the files in this order, allowing the two expected ALTER errors before continuing to the metadata query:

mariadb --batch --raw < setup.sql

mariadb --batch --raw < copy.sql

mariadb --batch --raw < inplace.sql

mariadb --batch --raw < metadata.sql

Actual result

The COPY operation returns error 1829 and correctly names the declared constraint:

ERROR 1829 (HY000): Cannot drop column 'ref': needed in a foreign key constraint 'fk_ref' of table `diag`.`child`

The subsequent INPLACE operation returns the same error, but identifies the constraint as the internal diag/child value:

ERROR 1829 (HY000): Cannot drop column 'ref': needed in a foreign key constraint 'diag/child' of table `diag`.`child`

The failed operations leave all four columns and the foreign-key metadata intact:

TABLE_NAME  COLUMN_NAME

child       id

child       ref

parent      id

parent      ref

TABLE_NAME  CONSTRAINT_NAME

child       fk_ref

Expected result

Both algorithms should reject the operation with error 1829 naming the SQL-visible constraint fk_ref. The observed problem is limited to the INPLACE diagnostic identity; the evidence does not show a loss of data or foreign-key enforcement.

This occurs when an INPLACE column drop reaches the foreign-key dependency diagnostic under a statement-local foreign-key-checks override.