Database Design and Primary Keys
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Questions and Answers

What type of primary key is recommended for easier handling?

  • Textual Key
  • Composite Attribute
  • Alphanumeric Key
  • Numerical Key (correct)
  • 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?

    Composite Attribute

    A primary key that includes a single attribute is known as a __________.

    <p>simple key</p> Signup and view all the answers

    Match the following terms related to primary keys:

    <p>Composite Attribute = Single attribute considered a primary key Simple Key = Multiple attributes forming a primary key Primary Key = Unique identifier for a record Numerical Key = Easier to handle primary key option</p> Signup and view all the answers

    Which of the following is an example of a multivalue attribute?

    <p>Phone number</p> Signup and view all the answers

    A complex attribute is simply an attribute that cannot have multiple values.

    <p>False</p> Signup and view all the answers

    What distinguishes a multivalue attribute from a single-valued attribute?

    <p>A multivalue attribute can have multiple values, while a single-valued attribute can only have one.</p> Signup and view all the answers

    An example of a multivalue attribute is ________.

    <p>email</p> Signup and view all the answers

    Match the following types of attributes with their definitions:

    <p>Multivalue Attribute = Can have multiple values Complex Attribute = A more complex version of an attribute</p> Signup and view all the answers

    What should be done with a multi-value attribute in a database design?

    <p>Create a new table and add a foreign key</p> Signup and view all the answers

    Each attribute in a composite attribute can be considered a candidate key.

    <p>True</p> Signup and view all the answers

    What is the purpose of creating a new table for multi-value attributes?

    <p>To maintain normalization and avoid data redundancy.</p> Signup and view all the answers

    To handle a multi-value attribute, it is necessary to create a new table and add a __________ key from the original table.

    <p>foreign</p> Signup and view all the answers

    Match the following database concepts with their definitions:

    <p>Composite Attribute = An attribute that consists of multiple sub-attributes Multi-value Attribute = An attribute that can have multiple values for a single record Candidate Key = An attribute that can uniquely identify a record in a table Foreign Key = An attribute that creates a relationship between two tables</p> Signup and view all the answers

    What does the TOP keyword do in a SQL query?

    <p>Retrieves a specific number of rows from a table</p> Signup and view all the answers

    The TOP keyword can be used with a query to return an unlimited number of records.

    <p>False</p> Signup and view all the answers

    Write a SQL query using the TOP keyword to retrieve the top 3 students by their marks.

    <p>SELECT TOP 3 fname, mark FROM student_DB ORDER BY mark DESC;</p> Signup and view all the answers

    The command SELECT TOP 2 fname, mark FROM student_DB ORDER BY mark _______ ; retrieves the top 2 rows based on marks.

    <p>DESC</p> Signup and view all the answers

    Match the SQL commands with their descriptions:

    <p>SELECT TOP 2 fname, mark FROM student_DB = Retrieves the top 2 students by marks. ORDER BY mark DESC = Sorts the results in descending order based on marks. SELECT * FROM student_DB = Retrieves all fields from the student database. DELETE FROM student_DB = Removes records from the student database.</p> Signup and view all the answers

    What does char(10) do in terms of memory allocation?

    <p>Reserves 10 bytes of memory regardless of actual string length</p> Signup and view all the answers

    varchar(n) uses the same amount of memory as char(n) regardless of the length of the string stored.

    <p>False</p> Signup and view all the answers

    What is the main advantage of using varchar(n) over char(n)?

    <p>It saves memory by using only the actual space needed for the string.</p> Signup and view all the answers

    char(10) reserves a fixed amount of memory while ______ uses memory based on the actual content length.

    <p>varchar(n)</p> Signup and view all the answers

    Match the following types of string data types with their characteristics:

    <p>char(10) = Reserves 10 bytes regardless of actual length varchar(n) = Reserves space based on actual string length</p> Signup and view all the answers

    What is the primary function of the AVG function?

    <p>Calculate the average mark for students</p> Signup and view all the answers

    The GROUP BY clause cannot be used in conjunction with aggregate functions.

    <p>False</p> Signup and view all the answers

    What does the GROUP BY clause do in SQL?

    <p>It groups rows that have the same values in specified columns into summary rows.</p> Signup and view all the answers

    The AVG function is often combined with ______ to calculate statistics specific to each group.

    <p>GROUP BY</p> Signup and view all the answers

    Match the SQL functions with their main purposes:

    <p>AVG = Calculates average value COUNT = Counts the number of rows SUM = Calculates total value MAX = Finds the maximum value</p> Signup and view all the answers

    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.

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