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Questions and Answers
What is a requirement for a primary key in a relational database?
What is a requirement for a primary key in a relational database?
What does referential integrity ensure in a relational database?
What does referential integrity ensure in a relational database?
How can controlled redundancy benefit a relational database?
How can controlled redundancy benefit a relational database?
What is the purpose of the SELECT operation in relational algebra?
What is the purpose of the SELECT operation in relational algebra?
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Which statement correctly defines a secondary key in a database?
Which statement correctly defines a secondary key in a database?
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What is the consequence of using NULL values in attributes of a database?
What is the consequence of using NULL values in attributes of a database?
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Which of the following is NOT a common relational algebra operator?
Which of the following is NOT a common relational algebra operator?
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What is the main goal of enforcing entity integrity rules in a database?
What is the main goal of enforcing entity integrity rules in a database?
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Why is it important to avoid NULL values in primary key attributes?
Why is it important to avoid NULL values in primary key attributes?
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What defines a foreign key in a relational database?
What defines a foreign key in a relational database?
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What does a composite key consist of in a relational database?
What does a composite key consist of in a relational database?
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Which of the following best describes the concept of functional dependence in a relational database?
Which of the following best describes the concept of functional dependence in a relational database?
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What is the primary role of keys in a relational database?
What is the primary role of keys in a relational database?
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Which type of integrity is maintained by ensuring all foreign keys match primary keys in another table?
Which type of integrity is maintained by ensuring all foreign keys match primary keys in another table?
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In relational algebra, which operation is used to combine rows from two or more tables based on a related column?
In relational algebra, which operation is used to combine rows from two or more tables based on a related column?
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Which of the following statements about tables in a relational database model is true?
Which of the following statements about tables in a relational database model is true?
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What does the data dictionary in a relational database typically contain?
What does the data dictionary in a relational database typically contain?
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Which type of join returns only matching rows from both tables involved?
Which type of join returns only matching rows from both tables involved?
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What characteristic of relational databases allows for changes in data structure without affecting the entire system?
What characteristic of relational databases allows for changes in data structure without affecting the entire system?
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Which operation yields only the rows that exist in both tables being combined?
Which operation yields only the rows that exist in both tables being combined?
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What is the purpose of using a LEFT OUTER JOIN in a relational database?
What is the purpose of using a LEFT OUTER JOIN in a relational database?
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What characteristic must tables have to be used in a UNION operation?
What characteristic must tables have to be used in a UNION operation?
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Which join type retains unmatched records from both tables, filling in nulls where necessary?
Which join type retains unmatched records from both tables, filling in nulls where necessary?
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What do the terms homonym and synonym signify in the context of a data dictionary?
What do the terms homonym and synonym signify in the context of a data dictionary?
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Which relational algebra operation yields all possible combinations of rows from two tables?
Which relational algebra operation yields all possible combinations of rows from two tables?
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In a relational database, what type of relationship is the 1:M relationship considered to be?
In a relational database, what type of relationship is the 1:M relationship considered to be?
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The DIVIDE operation in relational algebra enables which of the following?
The DIVIDE operation in relational algebra enables which of the following?
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What does the term 'referential integrity' in a relational database guard against?
What does the term 'referential integrity' in a relational database guard against?
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Which type of join requires explicit criteria to be defined for matching records?
Which type of join requires explicit criteria to be defined for matching records?
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In a relational database, what does an inner join specifically return?
In a relational database, what does an inner join specifically return?
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Which of the following must be true for a natural join to occur between two tables?
Which of the following must be true for a natural join to occur between two tables?
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What type of relationship should rarely exist in a relational database design?
What type of relationship should rarely exist in a relational database design?
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When breaking an M:N relationship into separate entities, what must be included?
When breaking an M:N relationship into separate entities, what must be included?
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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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Study Notes
Relational Database Model
- The relational database model uses a logical view of data.
- The model is based on tables that represent relations.
- Tables are implemented in a relational database management system (RDBMS).
- A table consists of rows (tuples) and columns (attributes).
- Each row in a table represents an entity.
- A table is a logical representation of the database structure.
- Data redundancy is handled by sharing common attributes between tables.
- The relational database model uses keys to identify rows uniquely.
- A key is a set of attributes that determine other attributes.
- Functional dependence indicates that the value of one attribute can determine the values of other attributes.
- A composite key is composed of multiple attributes.
- A key attribute is any attribute that is part of a key.
- A superkey uniquely identifies each row.
- A candidate key is a minimal superkey.
- A primary key uniquely identifies each row in the table.
- Each primary key must have unique values and cannot contain a null value.
- A null value represents an unknown, missing or a "not applicable" attribute value.
- Controlled redundancy exists when attribute values are duplicated for relational purposes.
- A foreign key references a primary key value in a related table.
- Referential integrity ensures that a foreign key is valid.
- A secondary key is used for data retrieval purposes.
- Indexing helps to improve database performance by providing an index for retrieval of data.
Relationships within the Relational Database
- A 1:M relationship is the ideal relationship in the relational model where one entity is related to many entities.
- A 1:1 relationship is rarely used and may indicate that two entities should be combined into one table.
- A M:N relationship cannot be implemented directly. This relationship can be achieved by creating a composite entity using foreign keys to link tables.
- A composite entity includes foreign keys from the primary keys of the tables to be linked.
Relational Set Operators
- Relational operators manipulate table contents and create new relations using relational algebra.
- SELECT retrieves rows based on certain criteria.
- PROJECT selects a subset of columns from a table.
- JOIN merges data from multiple tables based on common columns.
- UNION combines rows from two tables, excluding duplicates.
- INTERSECT returns rows that appear in both tables, excluding duplicates.
- DIFFERENCE returns rows that are in the first table excluding the rows found in the second table.
- PRODUCT returns all possible combinations of rows from two tables.
- DIVIDE returns values from a 2-column table(dividend) based on the presence of those values in a single-column table(divisor).
The Data Dictionary and System Catalog
- The Data Dictionary contains information about tables within the database.
- The system catalog provides metadata about all objects in the database.
- A homonym occurs when different attributes have the same name.
- A synonym occurs when the same attribute is referred to using different names.
Data Integrity
- Entity Integrity: ensures the uniqueness of each row within a table.
- Referential Integrity: ensures that the foreign keys in a table match existing primary keys in their corresponding table.
- These integrity rules can be enforced by the RDBMS or implemented within application design.
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Description
This quiz covers the fundamental concepts of the relational database model, including its structure based on tables, unique keys, and data redundancy handling. Understand the roles of attributes, tuples, and key types like primary and composite keys to reinforce your knowledge of RDBMS.
