CREATE TABLE financial_transactions (transaction_id NUMBER, account_id NUMBER, invoice_number NUMBER, transaction_type CLOB, transaction_date TIME, transaction_amount NUMBER, transaction_comment CLOB, other_transaction_details CLOB)
CREATE TABLE product_categories (production_type_code CLOB, product_type_description CLOB, vat_rating NUMBER)
CREATE TABLE accounts (account_id NUMBER, customer_id NUMBER, date_account_opened TIME, account_name CLOB, other_account_details CLOB)
CREATE TABLE invoices (invoice_number NUMBER, order_id NUMBER, invoice_date TIME)
CREATE TABLE order_items (order_item_id NUMBER, order_id NUMBER, product_id NUMBER, product_quantity CLOB, other_order_item_details CLOB)
CREATE TABLE customers (customer_id NUMBER, customer_first_name CLOB, customer_middle_initial CLOB, customer_last_name CLOB, gender CLOB, email_address CLOB, login_name CLOB, login_password CLOB, phone_number CLOB, town_city CLOB, state_county_province CLOB, country CLOB)
CREATE TABLE invoice_line_items (order_item_id NUMBER, invoice_number NUMBER, product_id NUMBER, product_title CLOB, product_quantity CLOB, product_price NUMBER, derived_product_cost NUMBER, derived_vat_payable NUMBER, derived_total_cost NUMBER)
CREATE TABLE orders (order_id NUMBER, customer_id NUMBER, date_order_placed TIME, order_details CLOB)
CREATE TABLE products (product_id NUMBER, parent_product_id NUMBER, production_type_code CLOB, unit_price NUMBER, product_name CLOB, product_color CLOB, product_size CLOB)

How many order items correspond to each order id?
SELECT order_id, COUNT(*) FROM order_items GROUP BY order_id
SELECT "order_id", COUNT(*) FROM "order_items" GROUP BY "order_id"