Sometimes when dropping a table in Oracle database by executing DROP TABLE SQL statement, Oracle may return the error ORA-02449 as below:

ORA-02449: unique/primary keys in table referenced by foreign keys.

The Oracle error is caused by the attempt to drop a table with unique or primary keys referenced by foreign keys in another table, or in other word, the table that is referenced as a parent table by a foreign key constraint in a parent-child relationship that established between two tables through a foreign key. Oracle does not allow to drop tables referenced by foreign keys of other tables without specifying the CASCADE CONSTRAINTS option in the DROP TABLE statement, or to drop the parent table without first removing the foreign key.

The solution and workaround for the error when you want to drop tables referenced by child tables, is to use the CASCADE CONSTRAINTS option in the DROP TABLE statement. For example:

DROP TABLE table_name CASCADE CONSTRAINTS;

The CASCADE CONSTRAINTS option in the DROP TABLE SQL statement will drop the FOREIGN KEY constraints of the child tables referenced.

Alternatively, you can manually drop and remove the foreign key key constraints in other tables before performing the DROP TABLE operations on the parent table, drop the foreign key constraints in other tables. To check what constraints are referencing a table in Oracle, use the following command:

SELECT * FROM USER_CONSTRAINTS WHERE TABLE_NAME = “table_name“;

To drop and delete the user constraints in Oracle use the following command in SQL*Plus, Toad or other SQL tools:

ALTER TABLE table_name DROP CONSTRAINT constraint_name;