SQL Views Chapter 3A

Appendix Objectives Learn basic SQL statements for creating views Learn basic SQL statements for using views Learn basic SQL statements for deleting views Understand the reasons for using views

SQL Views A SQL view is a virtual table that is constructed from other tables or views A view has no data of its own, but uses data stored in tables or other views Views are created using SQL SELECT statements Views are used in other SELECT statements just as if they were a table In some environments, the SQL statements that create the views may not contain an ORDER BY clause. If the results of a query using a view need to be sorted, the sort order must be provided by the SELECT statement that processes the view However, Oracle allows you to create the views that contain an ORDER BY clause

SQL CREATE VIEW Statement The SQL CREATE VIEW statement is used to create view structures. CREATE VIEW ViewName AS {SQL SELECT statement};

SQL CREATE VIEW Example Create a view to list the city and product name for each product ordered by its quantity: create view v_products as select city, pname as myname from products order by quantity;

Using an SQL SELECT Statement Once the view is created, it can be used in the FROM clause of SELECT statements just like a table. select * from v_products;

Some Uses for SQL Views Hide columns or rows Display results of computations Hide complicated SQL syntax Layer built-in functions

Using SQL Views: Hide columns or rows I Why do we want to hide columns/rows? 1. simplify results 2. security reasons prevent the display of sensitive data create view v_products as select city, pname as myname from products order by quantity; select * from v_products; CITYMYNAME Newarkcase Dallascomb Dallasfolder Duluthpen Duluthrazor Newarkbrush Dallaspencil

Using SQL Views: Hide columns or rows II How do we hide rows? Using WHERE clause Create a view to list the city and product name for cities whose names start from ‘D’ ordered by its quantity: create view v_products_2 as select city, pname as myname from products where city like 'D%' order by quantity ; CITYMYNAME Dallascomb Dallasfolder Duluthpen Duluthrazor Dallaspencil

Using SQL Views: Display results of computations – SQL Statement What are the benefits? 1. it saves users from having to know/remember how to calculate 2. it makes the results consistent Create a view to list the city and the total product quantities for each city: create view v_products_3 as select city, sum(quantity) as product_quantity from products group by city; select * from v_products_3; CITYPRODUCT_QUANTITY Dallas Duluth Newark303500

Using SQL Views: Hide complicated SQL syntax – SQL Statement Create a view to list the product ids and the total order quantity for each of them: create view v_products_4 as select p.pid, sum(o.qty) as order_quantity from products p, orders o where p.pid = o.pid group by p.pid; select * from v_products_4; PIDORDER_QUANTITY p04600 p p06400 p p p02400 p071400

Using SQL Views: Layering Computations and Built-in Functions 1 st SQL Statement Create a view to list the product ids, along with the product quantity and the total order quantity for each of them: create view v_products_5 as select p.pid, p.quantity, sum(o.qty) as order_quantity from products p, orders o where p.pid = o.pid group by p.pid, p.quantity; select * from v_products_5; PIDQUANTITYORDER_QUANTITY p p p p p p p

Using SQL Views: Layering Computations and Built-in Functions 2 nd SQL Statement Check those products that the total order quantity is over the product quantity: create view v_products_6 as select pid from v_products_5 where quantity < order_quantity;

Using SQL Views: Layering Computations and Built-in Functions Results insert into orders (ordno,month,cid,aid,pid,qty,dollars) values (1034,'jan','c001','a01','p01',700000,450.00); Select * from v_products_6; PID p01