--SELECT column_name(s)
--FROM table_name
--[WHERE condition]
--[GROUP BY column_name(s)]
--[HAVING condition]
--[ORDER BY column_name(s)];

--concatenation

--desc, asc, nulls last, nulls first

--conditions in WHERE clause:
--	<, >, =, <>, !=
--	between X and y
--	in, not in
--	is null, is not null

-- LIKE  _ - one character,  % - zero or more character

-- AND
-- OR

--Functions:
--	round()
--	trunc()
--	substr()
--	instr()
--	length()
--	to_char()
--	to_date()
--	month_between()
--	extract(... from ...)
--	lower()
--	upper()
--	replace()
--	nvl()

--	max()
--	min()
--	count()
--	avg()
--	sum()

-- sysdate  - current system date and time

-- subquery ! 

-- The different set operators are:
--	UNION
--	UNION ALL
--	MINUS
--	INTERSECT

-- ROWNUM	

-- INNER JOIN
-- LEFT OUTER JOIN
-- RIGHT OUTER JOIN 
-- FULL OUTER JOIN

-- FETCH FIRST n ROWS ONLY
-- FETCH FIRST n ROWS WITH TIES
-- OFFSET n ROWS FETCH NEXT m ROWS WITH TIES

-- DISTINCT

----------------------------------------------------------------------------
--1. List the title of the books which author is Erich Gamma

--2. Which books (title) were borrowed more than 2 times?

--3. Who is the oldest customer?

--4. Select the book items which theoretical value is less than the
--   price of the related book.

--5. Select the last borrowing.

--6. Number of books that were published between 1990 and 2000, or
--   whose price is between 1000 and 3000, or
--   whose topic is 'Science Fiction' and are shorter than 20 pages

--7. List only those years when more than one customer was born

--8. Select full name of student customers having currently some books 
--   borrowed (i.e., bring-back date is unknown), together with the titles
--   of the borrowed books and the book 
--   item IDs

--9. List the books which got more than 2000 royalty for the writing,
--   or which has more than two book_items.

--10. In the thriller topic which book has the lowest price?

--11. What is the sum of theoretical value of the book items for each
--    book id?

--12. List the topics which have less then 6 books.

--13. List the categories of the customers where the average membership fee is less than 3000.

--14. Create a view which lists for each books (id, title)
--    how many times was it borrowed.

--15. How many book items was borrowed by each customer (name)?

--16. List the books which title contains exactly two 'c'

--17. List the books which price is between 2000 and 5000.

--18. What are title of the books which price is less than 
--    the average price of the books which topic is Thriller,
--    or History?

--19. How many books belongs to each publisher?

--20. List the second 5 book items which has largest theoretical value