Assignment 1 Uploaded to course website Due next Tuesday, Sep 1, at 11:59pm

Chapter 1. Introduction to Database IST2102

Previous Lecture Potential problems with Lists – Deletion – Update – Insertion

A Long List to Several Small Lists IST2104 Two themes: Student, Course INFORMATION LOSS! Registration information is not in Student and Course tables

A Long List to Several Small Lists IST2105 PROBLEMS! One cell does NOT allow multiple values. (IMPORTANT! This rule is strictly enforced in database.) Two themes: Student, Course

A Long List to Several Small Lists IST2106 Student Entity Course Entity Student-Course Relationship Three themes: two entities and one relationship

A Long List to Several Small Lists IST2107 Student Course Registration Key points in splitting: 1. A table must be connected with other table(s) through shared column(s) Student  (StudentID)  Registration Course  (CourseID)  Registration 2. One cell can only have one value Revisit previous issues: Insert: A new student not taking any class Update: IST210 location changed Delete: Kate drops 230 Use above criteria to check whether you split the tables correctly!

Exercise IST2108 What are the modification problems (delete/insert/update) with this table? Split it into multiple tables. (Hint: do not lose information!)

Relational Databases A relational database stores information in tables. Each informational topic is stored in its own table In essence, a relational database will break-up a list into several parts. One part for each theme in the list IST2109

Answering Query: Putting the Pieces Back Together In our relational database, we broke apart our list into several tables. Somehow the tables must be joined back together In a relational database, tables are joined together using the value of the data IST21010

Query Relational Database: Using One Table IST21011 Student Table Course Table Registration Table Query 1: How many students take class 210? Answer: Check Registration Table to see many rows with CourseID as 210.  count = 4

Query Relational Database: Using Two Tables IST21012 Query 2: How many students take class taught by Marc? Student Table Course Table Registration Table Answer: Step 1. Check the CourseID taught by Marc in Course Table.  CourseID = 220 Step 2. See how many students taking class with CourseID 220 in Registration Table.  count = 2

Query Relational Database: Using Three Tables IST21013 Query 3: Who are the students taking class taught by Zihan? Student Table Course Table Registration Table Answer: Step 1. Check the CourseID taught by Zihan in Course Table.  CourseID = 210 Step 2. Get the StudentID taking class with CourseID 210 in Registration Table.  StudentID 101, 102, 103, 104 Step 3. Get the student names in Student Table with StudentID 101, 102, 103, 104.  Bob, Lisa, Sarah, Jim

Query Relational Database IST21014 Student Table Course Table Registration Table In a relational database, to answer a query, tables are joined together using the value of the data in the shared columns

Query Relational Database: Structured Query Language (SQL) Structured Query Language (SQL) is an international standard for creating, processing and querying databases and their tables IST21015 SELECTCount(StudentID) FROMCourse, Registration WHERECourse.CourseID = Registration.CourseID AND Course.Instructor = ‘Marc’ Query 2: How many students take class taught by Marc? Answer: Step 1. Check the CourseID taught by Marc in Course Table.  CourseID = 220 Step 2. See how many students taking class with CourseID 220 in Registration Table.  count = 2

Exercise (cont.) IST21016 After you split this table into multiple tables, answer following questions: Question 1: How many items purchased by Anderson? Question 2: What items purchased by customers in State College?

Sounds like More Work, Not Less A relational database is more complicated than a list However, a relational database minimizes data redundancy, preserves complex relationships among topics, and allows for partial data Furthermore, a relational database provides a solid foundation for user forms and reports IST21017

Chapter 1 Summary What is the problem with using a simple list to store the information? – Redundancy, Multiple themes  Modification issues What is the solution to replace a simple list? – Relational database – Break a simple long list to several tables; each table has its own theme How to query a relational database? – Join back the tables by the value of data through shared columns IST21018