The HR.DEPARTMENTS table is the parent of the HR.EMPLOYEES table. The EMPLOYEES.DEPARTMENT_ID column has foreign key constraint with the ON DELETE CASCADE option that refers to the DEPARTMETS .DEPARTM

DEPARTMENTS does not receive a table lock; only the specific parent row being deleted receives a row-level lock, so a table lock exclusively on DEPARTMENTS is incorrect.

Row-level locking on both tables would apply only if an index existed on EMPLOYEES.DEPARTMENT_ID (the child FK column), enabling Oracle to identify and lock only the affected child rows; without that index, a full table lock on EMPLOYEES is required.

A table lock on DEPARTMENTS alone is incorrect; the table lock caused by a missing child FK index is placed on the child table (EMPLOYEES), not on the parent table from which the row is deleted.

The index mentioned in the question is on DEPARTMENTS.DEPARTMENT_ID (the parent primary key column), not on EMPLOYEES.DEPARTMENT_ID (the child FK column); without an index on the child FK column, Oracle cannot efficiently locate child rows and must acquire a table lock on EMPLOYEES to process the cascade delete while blocking conflicting DML from other sessions - this lock still permits reads on the EMPLOYEES table.