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Questions and Answers
What is a primary key in a relation?
What is a primary key in a relation?
How is a primary key designated in a relation?
How is a primary key designated in a relation?
What does a relation in a relational database model represent?
What does a relation in a relational database model represent?
How is the structure of a relation expressed using shorthand notation?
How is the structure of a relation expressed using shorthand notation?
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What is an ER diagram used for in database design?
What is an ER diagram used for in database design?
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In the relational model, what is a relation composed of?
In the relational model, what is a relation composed of?
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What is a Data Dictionary in the context of database systems?
What is a Data Dictionary in the context of database systems?
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What is the purpose of a System Catalog in a database system?
What is the purpose of a System Catalog in a database system?
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Which of the following statements is true about a Data Dictionary?
Which of the following statements is true about a Data Dictionary?
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In a database system, what role does the System Catalog play during query processing?
In a database system, what role does the System Catalog play during query processing?
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How does a Data Dictionary differ from a System Catalog in a relational database management system?
How does a Data Dictionary differ from a System Catalog in a relational database management system?
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Which of the following best describes the primary function of a System Catalog in a database system?
Which of the following best describes the primary function of a System Catalog in a database system?
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What is the purpose of a data dictionary in a database system?
What is the purpose of a data dictionary in a database system?
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Which function does the system catalog serve in a database system?
Which function does the system catalog serve in a database system?
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What does the term 'homonym' refer to in the context of database attribute names?
What does the term 'homonym' refer to in the context of database attribute names?
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How does an outer join differ from an inner join?
How does an outer join differ from an inner join?
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In a database system, what is the purpose of an equijoin?
In a database system, what is the purpose of an equijoin?
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Which type of index ensures that each index key has only one associated row in a table?
Which type of index ensures that each index key has only one associated row in a table?
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What is the main function of an index key in a database system?
What is the main function of an index key in a database system?
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When using an equijoin, how are tables linked together?
When using an equijoin, how are tables linked together?
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What is an example of a synonym in a database system?
What is an example of a synonym in a database system?
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Why is data redundancy sometimes considered necessary?
Why is data redundancy sometimes considered necessary?
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Study Notes
Relational Database Models
- A relational database model represents data in the form of tables based on mathematical theory.
- A relation is a named, two-dimensional table of data, consisting of a set of named columns and an arbitrary number of unnamed rows.
Relational Algebra
- Relational algebra defines a theoretical way of manipulating table contents using relational operators.
- Relational algebra operators on existing relations produce new relations.
- Relational algebra operators include:
- SELECT: yields all values for all rows in a table that satisfy a given condition.
- PROJECT: yields all values for selected attributes - a vertical subset of a table.
- JOIN: combines all rows from two tables, excluding duplicate rows.
- UNION: yields all rows in one table that are not found in the other table.
- DIFFERENCE: yields all rows in one table that are not found in the other table.
- PRODUCT (or CARTESIAN PRODUCT): yields all possible combinations of rows from two tables.
- DIVIDE: uses one 2-column table as the dividend and one single-column table as the divisor.
Relational Set Operators
- Natural join: links tables by selecting rows with common values in common attributes (join columns).
- Equijoin: links tables on the basis of an equality condition that compares specified columns.
- Theta join: a comparison operator other than equal is used.
- Inner join: only returns matched records from the tables that are being joined.
- Outer join: returns all matched records (as an inner join) but returns the unmatched records from one of the tables.
- Left outer join: yields all of the rows in the CUSTOMER table, including those that do not have a matching value in the AGENT table.
- Right outer join: yields all of the rows in the AGENT table, including those that do not have matching values in the CUSTOMER table.
Data Dictionary and System Catalog
- Data dictionary: provides detailed accounting of all tables found within the user/designer-created database.
- System catalog: contains metadata and detailed system data dictionary that describes all objects within the database.
Homonyms and Synonyms
- Homonym: indicates the use of the same name to label different attributes.
- Synonym: indicates the use of different names to describe the same attribute.
Data Redundancy and Indexes
- Data redundancy: leads to data anomalies and can destroy the effectiveness of the database.
- Foreign keys: control data redundancies by using common attributes shared by tables.
- Indexes: an orderly arrangement to logically access rows in a table.
- Index key: the index's reference point that points to data location identified by the key.
- Unique index: an index in which the index key can have only one pointer value (row) associated with it.
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Description
Test your knowledge of SQL joins and relational algebra with this quiz! Questions cover topics like SELECT, PROJECT, JOIN, INTERSECT, UNION, and more from Chapter 3 of relational database models.
