chapter02

# chapter02 - Concepts of Database Management Fifth Edition...

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Concepts of Database  Concepts of Database  Management, Fifth Edition Management, Fifth Edition Chapter 2:  Chapter 2:  The Relational Model 1: The Relational Model 1: Introduction, QBE, and Introduction, QBE, and Relational Algebra Relational Algebra

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2 2 Objectives Describe the relational model Understand Query-by-Example (QBE) Use Criteria in QBE Create Calculated Columns in QBE Calculate Statistics in QBE
3 2 Objectives (con’t.) Sort data in QBE Join Tables in QBE Update data using QBE Understand relational algebra

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4 2 Relational Databases Collection of tables Each entity in own table Attributes are fields (columns) in table Relationships are common columns in two or more tables Order of rows and columns is immaterial Repeating groups are not permitted Entries with repeating groups are unnormalized
5 2 Premiere Products Sample Data

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6 2 Premiere Products Sample Data
7 2 Relations Two dimensional table in which: Entries are single-valued Each column (field or attribute) has a distinct name All values in a column represent the same attribute Order of columns is immaterial Each row (record or tuple) is distinct Order of rows is immaterial

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8 2 An Unnormalized Relation Relational Database – a collection of relations Unnormalized relation When a structure satisfies all the properties of a relation except for the first item Some of the entries contain repeating groups and thus are not single-valued
9 2 Database Structure Representation Write the name of the table followed by a list of all columns within parentheses Each table should appear on its own line Use the notation, tablename.columnname, with duplicate column names within a database Using this combination qualifies column names Primary key – the column or collection of columns that uniquely identifies a given row in a table

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10 2 Query-by-Example (QBE) Query Questions represented in a way the DBMS can recognize and process QBE Visual approach to writing queries Used in MS-Access
11 2 Figure 2.3: An Example of Simple Queries

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12 2 Figure 2.4: Simple Queries (con’t.)
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