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. Conceptual Data Model Physical Data Model 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 Data does not physically exist (no storage) 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 loop; exception when incorrect_first_name then dbms-output.put_line (“Wrong spelling.”); end;

Example of Function P4.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 ship IN date); end; /

Example of Relational/Object-Oriented Database Structure

References: http://www.w3schools.com/sql/sql_join.asp Oracle Book