DROP TABLE customers;
 
CREATE TABLE customers (
first_name varchar2(100),
last_name varchar2(100),
country varchar2(20),
full_address CLOB,
employees NUMBER,
start_date DATE
);
 
INSERT INTO customers (first_name, last_name, country, full_address, employees, start_date) VALUES ('John', 'Smith', 'USA', '10 Long Road', 4, '12-APR-2010');
INSERT INTO customers (first_name, last_name, country, full_address, employees, start_date) VALUES ('Sally', 'Jones', 'USA', '50 Market Street', 10, '04-JUL-2011');
INSERT INTO customers (first_name, last_name, country, full_address, employees, start_date) VALUES ('Steve', 'Brown', 'Canada', '201 Flinders Lane', 15, '21-MAR-2009');
INSERT INTO customers (first_name, last_name, country, full_address, employees, start_date) VALUES ('Mark', 'Allan', 'UK', '8 Smith Street', 23, '1-FEB-2001');
INSERT INTO customers (first_name, last_name, country, full_address, employees, start_date) VALUES ('Adam', 'Cooper', 'USA', '14 Wellington Road', 55, NULL);
INSERT INTO customers (first_name, last_name, country, full_address, employees, start_date) VALUES ('Josh', 'Thompson', NULL, '80 Victoria Street', 1, '10-FEB-2012');
INSERT INTO customers (first_name, last_name, country, full_address, employees, start_date) VALUES ('Peter', 'Manson', 'France', '5 Johnson St', NULL, '16-OCT-2012');
INSERT INTO customers (first_name, last_name, country, full_address, employees, start_date) VALUES (NULL, '', NULL, '155 Long Road', NULL, '16-OCT-2012');
 
SELECT * FROM customers;
 
 
--Example 1
 
SELECT first_name, last_name, COALESCE(first_name, last_name) AS coal
FROM customers;
 
--Example 2
 
SELECT country, last_name, COALESCE(country, last_name) AS coal
FROM customers;
 
 
--Example 3
SELECT first_name, last_name, country, COALESCE(first_name, last_name, country) AS coal
FROM customers
WHERE start_date = '16-OCT-2012';
 
--Example 4
SELECT first_name, full_address, employees, start_date, COALESCE(first_name, full_address, employees, start_date) AS coal
FROM customers;
 
--Example 5
SELECT first_name, last_name, COALESCE(NULL, NULL, first_name, NULL, NULL, NULL, last_name) AS coal
FROM customers;
 
--Example 6
SELECT first_name, COALESCE('', first_name) AS coal
FROM customers;
 
--Example 7
SELECT start_date, COALESCE(start_date, SYSDATE) AS coal
FROM customers;
 
--Example 8
SELECT country, LENGTH(country), employees
FROM customers
WHERE COALESCE(employees, LENGTH(country)) > 4