Utilizing subqueries in sql. Displaying no output - sql

Question

I have a task of retrieving the first and last names of customers where their orders have not shipped out. Below is the tables made to get this result ↓↓↓
CREATE TABLE employees
(
employee_id INT NOT NULL,
last_name VARCHAR(20) NOT NULL,
first_name VARCHAR(20) NOT NULL,
manager_id INT,
CONSTRAINT employees_pk PRIMARY KEY (employee_id),
CONSTRAINT emp_fk_mgr
FOREIGN KEY (manager_id) REFERENCES employees(employee_id)
);
CREATE TABLE orders
(
order_id INT NOT NULL,
customer_id INT NOT NULL,
order_date DATE NOT NULL,
shipped_date DATE,
employee_id INT,
CONSTRAINT orders_pk PRIMARY KEY (order_id),
CONSTRAINT orders_fk_customers
FOREIGN KEY (customer_id) REFERENCES customers (customer_id),
CONSTRAINT orders_fk_employees
FOREIGN KEY (employee_id) REFERENCES employees (employee_id)
);
CREATE TABLE order_details
(
order_id INT NOT NULL,
item_id INT NOT NULL,
order_qty INT NOT NULL,
CONSTRAINT order_details_pk PRIMARY KEY (order_id, item_id),
CONSTRAINT order_details_fk_orders
FOREIGN KEY (order_id) REFERENCES orders (order_id),
CONSTRAINT order_details_fk_items
FOREIGN KEY (item_id) REFERENCES items (item_id)
);
Currently, I have the following query made up, but it keeps generating No Output.
SELECT c.customer_first_name
FROM order_details od
JOIN orders o ON od.order_id = o.order_id
JOIN customers c ON o.customer_id = c.customer_id
WHERE c.customer_id IN (SELECT shipped_date FROM orders WHERE shipped_date IS NULL);
Can someone help me to get the result I need?

Answer 1

Presumably, your customers are not dates and you actually intend:
WHERE c.customer_id IN (SELECT o.customer_id FROM orders o WHERE shipped_date IS NULL)