国外的大学开设的数据库课程的课件
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2023-05-15
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Introduction to Databases & SQL
CSCE 156 - Introduction to Computer Science II
Christopher M. Bourke
cbourke@cse.unl.edu
Introduction to Databases & SQL
I
Lifetime of a program is short-lived
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Applications perform small ephemeral operations
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Can crash and die
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Programs may be limited to sessions or even single requests
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Need a way to persist data or program state across program lives
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Databases provide such a means
Motivating Example I
Flat Files
Consider the following data, stored in a flat file:
Course Course Name Student NUID Email
waits, tom 11223344 tomwaits@hotmail.com
CSCE 156 Intro to CSII Lou Reed 11112222 reed@gmail.com
CSCE 156 Intro to CSII Tom Waits 11223344 twaits@email.com
CSCE 230 Computer Hardware Student, J. 12345678 jstudent@geocities.com
CSCE 156 Intro to CSII Student, John 12345678 jstudent@geocities.com
CSCE 230 Computer Hardware Student, J. 12345678 jstudent@geocities.com
CSCE 235 Discrete Math Student, John 12345678 jstudent@geocities.com
CSCE 235 Discrete Math Tom Waits 11223344 twaits@email.com
NONE Null Tom Waits 11223344 twaits@email.com
Table : Course enrollment data
Motivating Example II
Flat Files
Problems?
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Repetition of data
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Incomplete data
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Integrity of data
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Organizational problems: any aggregation requires processing all
records
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Updating information is difficult (must enumerate all possible
changes, side effects so that information is not lost)
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Formatting Issues
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Concurrency Issues
Relational Databases I
Key Aspects
Solution: Relational Database Systems (RDBS) or Relational Database
Management System (RDMS)
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Stores data in tables
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Tables have a unique name and type description of its fields (integer,
string)
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Each column stores a single piece of data (field)
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Each row represents a record (or object!)
Relational Databases II
Key Aspects
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Each row may have a unique primary key which may be
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Automatically incremented
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An external unique identifier: SSN, ISBN, NUID
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Based on a combination of fields (Geographical data)
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Rows in different tables are related to each other through foreign keys
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Order of rows/columns is meaningless
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