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Questions and Answers
What type of primary key is recommended for easier handling?
What type of primary key is recommended for easier handling?
A composite attribute cannot be a primary key if it contains only one attribute.
A composite attribute cannot be a primary key if it contains only one attribute.
False
What is a primary key that consists of multiple attributes called?
What is a primary key that consists of multiple attributes called?
Composite Attribute
A primary key that includes a single attribute is known as a __________.
A primary key that includes a single attribute is known as a __________.
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Match the following terms related to primary keys:
Match the following terms related to primary keys:
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Which of the following is an example of a multivalue attribute?
Which of the following is an example of a multivalue attribute?
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A complex attribute is simply an attribute that cannot have multiple values.
A complex attribute is simply an attribute that cannot have multiple values.
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What distinguishes a multivalue attribute from a single-valued attribute?
What distinguishes a multivalue attribute from a single-valued attribute?
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An example of a multivalue attribute is ________.
An example of a multivalue attribute is ________.
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Match the following types of attributes with their definitions:
Match the following types of attributes with their definitions:
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What should be done with a multi-value attribute in a database design?
What should be done with a multi-value attribute in a database design?
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Each attribute in a composite attribute can be considered a candidate key.
Each attribute in a composite attribute can be considered a candidate key.
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What is the purpose of creating a new table for multi-value attributes?
What is the purpose of creating a new table for multi-value attributes?
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To handle a multi-value attribute, it is necessary to create a new table and add a __________ key from the original table.
To handle a multi-value attribute, it is necessary to create a new table and add a __________ key from the original table.
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Match the following database concepts with their definitions:
Match the following database concepts with their definitions:
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What does the TOP
keyword do in a SQL query?
What does the TOP
keyword do in a SQL query?
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The TOP
keyword can be used with a query to return an unlimited number of records.
The TOP
keyword can be used with a query to return an unlimited number of records.
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Write a SQL query using the TOP
keyword to retrieve the top 3 students by their marks.
Write a SQL query using the TOP
keyword to retrieve the top 3 students by their marks.
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The command SELECT TOP 2 fname, mark FROM student_DB ORDER BY mark _______ ;
retrieves the top 2 rows based on marks.
The command SELECT TOP 2 fname, mark FROM student_DB ORDER BY mark _______ ;
retrieves the top 2 rows based on marks.
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Match the SQL commands with their descriptions:
Match the SQL commands with their descriptions:
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What does char(10)
do in terms of memory allocation?
What does char(10)
do in terms of memory allocation?
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varchar(n)
uses the same amount of memory as char(n)
regardless of the length of the string stored.
varchar(n)
uses the same amount of memory as char(n)
regardless of the length of the string stored.
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What is the main advantage of using varchar(n)
over char(n)
?
What is the main advantage of using varchar(n)
over char(n)
?
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char(10)
reserves a fixed amount of memory while ______
uses memory based on the actual content length.
char(10)
reserves a fixed amount of memory while ______
uses memory based on the actual content length.
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Match the following types of string data types with their characteristics:
Match the following types of string data types with their characteristics:
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What is the primary function of the AVG
function?
What is the primary function of the AVG
function?
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The GROUP BY
clause cannot be used in conjunction with aggregate functions.
The GROUP BY
clause cannot be used in conjunction with aggregate functions.
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What does the GROUP BY
clause do in SQL?
What does the GROUP BY
clause do in SQL?
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The AVG
function is often combined with ______ to calculate statistics specific to each group.
The AVG
function is often combined with ______ to calculate statistics specific to each group.
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Match the SQL functions with their main purposes:
Match the SQL functions with their main purposes:
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Study Notes
Database Design
- Database design involves analysis, entity-relationship diagrams (ER-diagrams), schemas, DDL (Data Definition Language), and DML (Data Manipulation Language).
- Analysis: The initial phase of database design, examining data requirements and relationships.
- Entity-Relationship Diagrams (ER-diagrams): Visual representations of entities (objects) and relationships between them. Attributes describe the properties of entities.
- Schema: Structured representation of the database design.
- DDL (Data Definition Language): Used to define the structure and schema of a database (e.g., create, drop, alter tables).
- DML (Data Manipulation Language): Used to manipulate data within a database (e.g., insert, delete, update, and select).
Entity Types
- Entity: A real-world object or concept, like a student, course, or instructor.
- Key Attributes: Unique identifiers for entities (e.g., student ID).
- Attributes: Properties or characteristics that describe an entity, such as name, major, grade.
Relationships
-
Relationships: Associations between entities, expressed as 1:1, 1:M, or M:M.
- 1:1 (one-to-one): One entity is related to exactly one other entity.
- 1:M (one-to-many): One entity is related to many other entities.
- M:M (many-to-many): Many entities can be related to many other entities.
Attributes
- Single Attribute: A single piece of data (e.g., student name).
- Composite Attribute: A combination of several single attributes to represent a complex attribute (e.g., full address containing street, city, and zip code).
- Multi-valued Attribute: Represents several values for an attribute (e.g., phone numbers for a person).
- Derived Attribute: Computed from other attributes (e.g., calculating age from birthdate).
- Key Attribute: Unique identifiers for an entity (e.g., a student ID).
- Foreign Key: An attribute in one table that refers to the primary key of another table.
Cardinality Ratio
- Cardinality Ratio: The numeric relationship describing the number of instances in one entity in relation to the other entity. It explains the relationship between multiple tables.
Participation Constraints
- Total participation: Every entity in one set must be related to another entity set.
- Partial participation: Not every entity in one set is related to an entity in another entity set.
Relationship Types
- Binary relationships: Relationships involving two entities.
- Unary/Recursive relationships: Relationships between instances of the same entity set (e.g., an instructor supervising another instructor).
- Ternary relationships: Relationships involving three entities.
Entities
- Strong Entity: An entity that can exist independently. They have a unique attribute (primary key).
- Weak Entity: An entity that cannot exist independently of another entity (or strong entity). They have partial keys (not unique attributes) and depend on other entities for existence.
Converting ERDs to Relational Schemas
- Mapping algorithms are used for converting ERDs to relational schemas. Entity types become tables and relationships between entities become foreign keys in related tables.
SQL and Database Management Systems (DBMS)
- SQL (Structured Query Language): A language used to interact with databases (create, read, update, and delete data).
- DBMS (Database Management System): Software that manages the creation, maintenance, and access of a database.
Table Constraints
- Column data types: The specific type of data that column holds (e.g., integer, string, date, numeric).
- Not Null: Indicates a column cannot have a Null value.
- Unique: Ensures that values entered in a column are unique.
- Primary key: A unique key (often a column) that uniquely identifies each row in a table.
- Foreign key: A key in one table that references the primary key of another table.
- Check: A condition that restricts the values that can be entered in a column.
- Default: A value that is automatically assigned to a column if no other value is entered.
- Constraints: Rules or restrictions to enforce integrity and data validation in a table. Primary key, foreign key and unique are examples of constraints.
DML Commands
- Insert: Adds new data to a table.
- Select: Retrieves data from a table.
- Update: Modifies existing data in a table.
- Delete: Removes data from a table.
- Aggregate Functions: Calculate summary values (e.g., count, average, sum, min, max) for columns in a table.
- Grouping: Group rows with the same values in a column (usually used with aggregate functions).
- Ordering: Sort rows by values in one or more columns.
- Filtering: Filter (using conditions) rows in a table to return only those that meet the conditional criteria.
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Description
Test your understanding of primary keys in database design with this quiz. Explore concepts like composite attributes, multivalue attributes, and the importance of creating new tables for multi-value attributes. Perfect for students in database management courses.