Chapter 4
Lecture 2
SQL
4.6 – 4.9
Joining Multiple Tables
Display book titles and the first and last names of customers who ordered them
Traditional method
JOIN method
Aggregate Functions
Display total profit from books sold
Display total profit from books sold on order 1007
Display average profit by category
Subqueries
Display title, retail price, category, and the corresponding category average price for each
book that has a higher-than-average price than other books in its category
Select title, retail, category, cataverage
From books natural join (select category, avg(retail) cataverage
From books
Group by category);
Display categories and average profit values for those categories that have a higher
average profit than the Literature category does
Select category, avg(retail-price) “Average Profit”
From books
Group by category
Having avg(retail-price) > (select avg(retail-price)
From books
Where category = “LITERATURE”);
Data Manipulation
Inserting new records
INSERT INTO tablename [(columname, ...)]
VALUES (datavalue, ...);
Insert a record for yourself into the Customers table.
Insert a new book into the Books table
Make an order for yourself (insert record into the database)
Modifying Existing Rows
UPDATE tablename
SET columnname = new_datavalue
[WHERE condition];
Modify your REFERRED, or ADDRESS info; or
Modify the pricing info of the books you entered
Deleting Rows
DELETE FROM tablename
[WHERE condition];
Delete a (few) row(s) you’ve entered.
ROLLBACK
Views
Creating a Simple View
A simple view is created from a subquery that only references one table and doesn’t
include a group function, or GROUP BY clause. (It’s possible to update through a
simple view.)
CREATE VIEW inventory
AS SELECT isbn, title, price
FORM books
WITH READ ONLY;
The last clause is used to prevent data from being modified by the user of this view.
Creating a Complex View
A complex view is one that is not simple.
CREATE VIEW prices
AS SELECT isbn, title, cost, retial, retail-price profit, name
FORM books NATURAL JOIN publishers;
The following limitations apply to DML operations on the view prices. No changes can
be made to
- the field profit: a calculated field
- the name field: a column from a non key-preserved table
In addition, no changes may be made to views with a group function or a group by
clause.
Top-N Analysis
SELECT columnname, ...
FORM subquery
WHERE ROWNUM <= N;
Top five most-profitable books may be retrieved by
SELECT title, profit
FORM (SELECT title, retail-cost profit
FROM books
ORDER BY retail-cost DESC)
WHERE ROWNUM <= 5;