CREATE TABLE foo ( x int PRIMARY KEY );
CREATE TABLE bar (
  x int,
  CONSTRAINT asdf FOREIGN KEY (x) REFERENCES foo(x)
);


MariaDB [test]> DROP TABLE foo;
ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails

# CREATE TABLE foo ( x int PRIMARY KEY );
# CREATE TABLE bar ( x int REFERENCES foo );
# DROP TABLE foo CASCADE;
NOTICE:  drop cascades to constraint bar_x_fkey on table bar
DROP TABLE

CREATE TABLE foo
(
  x int PRIMARY KEY
);

CREATE TABLE bar
(
  x int,
  CONSTRAINT asdf FOREIGN KEY (x) REFERENCES foo(x) ON DELETE CASCADE
);

INSERT INTO foo VALUES (3), (45), (7);
INSERT INTO bar VALUES(3), (3), (45), (7), (7);

DELETE FROM foo WHERE x = 3;

SELECT * FROM bar;

 x
 7
 7
45

ERROR:  cannot drop table foo because other objects depend on it
DETAIL:  constraint asdf on table bar depends on table foo
HINT:  Use DROP ... CASCADE to drop the dependent objects too

DROP TABLE foo CASCADE;