How does mysql determine whether a foreign key exists before deleting it?

mysql

As mentioned, how to first determine whether the foreign key exists and then delete it, like
if EXISTS((SELECT COUNT(*) FROM information_schema.KEY_COLUMN_USAGE where constraint_name='fk_emp_dept_id') > 0)
alter table org_employee drop foreign key fk_emp_dept_id;
Also,
if EXISTS((SELECT COUNT(*) FROM information_schema.KEY_COLUMN_USAGE where constraint_name='fk_emp_dept_id') > 0)
BEGIN
alter table org_employee drop foreign key fk_emp_dept_id;
END
will report an error, please give me an answer

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