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Introduction to Database

Introduction to Database. Lei Yang Computer Science Department. An example. Why we use database?. You have a company with more than 10000 employees… Someday, you want to find out The average salary of employees who own Ph.d degree… The average age of your company… …. Manually?. No!.

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Introduction to Database

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  1. Introduction to Database Lei Yang Computer Science Department

  2. An example Why we use database? • You have a company with more than 10000 employees… • Someday, you want to find out • The average salary of employees who own Ph.d degree… • The average age of your company… • … Manually? No!

  3. Manage Employees in the Company • Employee Information • Name: Jack, Ram… • Gender: Male, Female • Degree: Bachelor, Master, Ph.d… • Department: HR, Market Department… • Job: Engineer, Salesman, … • Salary: 10k, 15k, … • Manager: Jason, … • … Problem: How to store these data?

  4. Table • Database Store Data in Tables COLUMN A field or an attribute ROW: a record Text Currency NUMBER Question: how to distinguish two employee with nearly the same information?

  5. Primary Key Primary Key Unique

  6. Data Type - 1 • Text • Stores text, numbers, or a combination of both, up to 255 characters long. Text fields are the most common of all data types. • Memo • Stores long text entries up to 64,000 characters long. • Number: int, float… • Date/Time • Stores dates, times, or both. • Currency • Stores numbers and symbols that represent money.

  7. Data Type - 2 • AutoNumber • Automatically fills in a unique number for each record. AutoNumber is used as primary key in many tables. • Yes/No • Stores only one of two values, such as Yes or No, True or False, etc. • OLE Object • Stores objects created in other programs such as a graphic, Excel spreadsheet, or Word document. • Hyperlink • Stores clickable links to files on your computer, on the network, or to Web pages on the Internet.

  8. Data Type - 3 • Lookup Wizard • A wizard that helps you create a field whose values are selected from a table, query, or a preset list of values.

  9. Query Answer in Database-1 • Query: Find out the names of all employees whose salary is greater than 12k?

  10. Query in Database-2 SELECTION PROJECTION James, Mary

  11. Query in Database-3 • SELECTION • Selecting records which satisfies certain conditions • Projection • Projecting a field into query simply means including it in the query

  12. Query in Database-4 • SQL(Structured Query Language) • Used in Database • A simple structure • SELECT <fields> • FROM <table> • WHERE <condition> An example show how it works

  13. Query in Database-4 • Query: Find out the names of all employees whose salary is greater than 12k? • SELECT • FROM • WHERE PROJECTION Name <field> <table> Employee Salary > 12k <condition> SELECTION • SELECTION: Selecting records which satisfies certain conditions. • PROJECTION: Projecting a field into query simply means including it in the query

  14. Query in Database-5 • How to search in two tables? Find out the name of employees in HR?

  15. Query in Database-6 Department Employee • Cartesian Product X =

  16. Query in Database-7 • SELECT <Name> • FROM <Employee, Department> • WHERE <DepartmentName = “HR” and • Employee.DptID = Department.DptID> JOIN Cartesian Product

  17. Query in Database-8 • Operators in conditions

  18. Query in Database-9 • Aggregate Function How many employees are there in department D004?

  19. Query in Database-10 • SELECT count(EmployeeID) • FROM <Employee> • HAVING DptID = “D004” Aggregate Function

  20. Query in Database-11 • Aggregate Functions

  21. Question

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