Database Technology

Jing Shen

Topics

• Introductions

• SQL Statements

• View

• Store Procedure/Functions

• Triggers

• Example of Object-Oriented Relational DB

SQL has several parts

• DDL – Data Definition Language

• DML – Data Manipulation Language

• Embedded SQL – Designed for use within a host language

• Authorization or DCL – Data Control Language

• Integrity

Define Database and DBMS

• Database: A collection of related data.

• DBMS: A set of programs that enable users to create and maintain a database.

Data Models

• It is a collection of concepts that can be used to describe the structure of a database.

1. Conceptual Data Model

2. Physical Data Model

3. Representational (or Implementation) Data Model

Three types of Representational Data Model

• Relational Data Model

• Hierarchical Data Model

• Network Data Model

DML (Data Manipulation Language)

• INSERT – insert into table_name[(column, [column]…)] {values ( expr[,expr]…) | subquery}

• DELETE – delete [From] table_name [WHERE condition]

• Update – update table_name set field = [, field = , …] [ WHERE condition ];

Transaction

• A transaction is a sequence of SQL statements that Oracle treats as a single unit.

• COMMIT;

• ROLLBACK;

“autocommit” is set on

SQL Join

• The INNER JOIN returns all rows from both tables where there is a match.

• Example: SELECT Employees.Name, Orders.Product FROM Employees INNER JOIN Orders ON Employees.ID = Orders.ID

Joining a table to itself

• Return all the results where the attribute is in the same table.

Example: select s1.s#, s2.s# from s s1, s s2 where s1.city = s2.city and s1.s#<s2.s#;

Get all pairs of supplier numbers such that the two suppliers are located in the same city.

Continues…

• The LEFT JOIN returns all the rows from the first table (Employees), even if there are no matches in the second table (Orders). Example: SELECT Employees.Name, Orders.Product FROM Employees LEFT JOIN Orders ON Employees.ID = Orders.ID

Continues…

• The RIGHT JOIN returns all the rows from the second table (Orders), even if there are no matches in the first table (Employee). Example: SELECT Employees.Name, Orders.Product FROM Employees RIGHT JOIN Orders ON Employees.ID = Orders.ID

View

• A view is logical table

1. Data does not physically exist (no storage)

2. Views are defined in terms of base tables “created by SELECT statement”

Store Procedures

• It allows for sharing o PL/SQL code by different applications running at different places. Syntax:create [or replace] procedure <proc-name> [(<parameter-list>)] as <declarations> begin

<executable-section>end;

Function: create [or replace] function <func-name> [(<parameter-list>)] return <datatype> as

Example of how user defined exceptions

Set serveroutput on;declare

incorrect_first_name exception;fname employee.first_name%type;lname employee.last_name%type;cursor a is select last_name, first_name from employee;begin

open a;loop

fetch a into lname, fname;dbms_output.put_line (fname);if (a%notfound) then exit;end if;if (fname = ‘ELINOR’) then

raise incorrect_first_name;end if;

end loop;exception

when incorrect_first_name then dbms-output.put_line (“Wrong spelling.”);end;

Example of FunctionP4.sql:DECLARE enum customers.cno%type; total number(10,2); status boolean;

function total_emp_sales( emp_no IN employees.eno%type) return number is sales number; begin select sum(price*qty) into sales from orders,odetails,parts where orders.eno = emp_no and orders.ono = odetails.ono and odetails.pno = parts.pno; return (sales); end;

BEGIN enum := 1000; total := total_emp_sales(enum); DBMS_OUTPUT.PUT_LINE('Total sales for employee ' || enum || ' is ' || total);END;/

Trigger

• It is a mechanism that automatically executes a specified PL/SQL block when a triggering event occurs on a table. The triggering event may be one of insert, delete, or update.

Example of Triggers

CREATE OR REPLACE TRIGGER delete_orders

BEFORE DELETE ON orders

FOR EACH ROW

BEGIN

DELETE FROM odetails WHERE ono = :old.ono;

END;

/

Packages

• A package is a group of related PL/SQL objects (variables, constants, types, and cursors), procedures, and functions that is stored in the database.

• It consists of two parts: Package specification and the package body.

Example of Package

create or replace package process_orders as procedure add_order_details (onum IN odetails.ono%type, pnum IN odetails.pno%type, quantity IN odetails.qty%type); procedure add_order (onum IN orders.ono%type, cnum IN orders.cno%type, enum IN orders.eno%type, receive IN date); procedure ship_order (onum IN orders.ono%type, ship IN date);end;/

Example of Relational/Object-Oriented Database Structure

References:

• http://www.w3schools.com/sql/sql_join.asp

• Oracle Book