https://www.udemy.com/course/plsql-by-example/learn/lecture/3169110#overview
DECLARE
customerId number := 10;
customerName varchar2(50);
customerAddress varchar2(50);
BEGIN
SELECT first_name, country INTO customerName, customerAddress
FROM customer
WHERE customer_id := customerId;
END;
DECLARE
customerId customer.customer_id%type := 10;
customerName customer.first_name%type;
customerAddress customer.country%type;
-- 이렇게 해두면 customer의 country 타입이 변하는 경우에도
BEGIN
SELECT first_name, country INTO customerName, customerAddress
FROM customer
WHERE customer_id := customerId;
END;