Database Design Fundamentals

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Questions and Answers

What are the three main components involved in database design?

Analysis, Entity Relationship Diagram (ERD), and Relational Schema

What is the difference between a composite attribute and a multivalue attribute?

  • A composite attribute is a group of attributes representing a single concept, while a multivalue attribute is a single attribute that can have multiple values. (correct)
  • There is no difference between a composite attribute and a multivalue attribute.
  • A composite attribute is a single attribute that can have multiple values, while a multivalue attribute is a group of attributes representing a single concept.
  • A composite attribute has a dependency on other attributes, while a multivalue attribute stands alone.

Which of the following is not a type of cardinality ratio?

  • 1:M
  • 1:N (correct)
  • 1:1
  • M:N

A weak entity is dependent on a strong entity for its existence.

<p>True (A)</p> Signup and view all the answers

The process of converting an ERD into a relational schema is called ______ mapping.

<p>Relational Schema</p> Signup and view all the answers

What is the primary purpose of a primary key in a relational schema?

<p>To uniquely identify each row in a table.</p> Signup and view all the answers

What are the two main types of SQL commands used in database management?

<p>DDL (Data Definition Language) and DML (Data Manipulation Language)</p> Signup and view all the answers

Which of the following is not a DDL command?

<p>update (A)</p> Signup and view all the answers

What is the difference between char(n) and varchar(n) data types?

<p><code>char(n)</code> stores fixed-length strings, reserving memory for the specified length, while <code>varchar(n)</code> stores variable-length strings, using only the actual space needed.</p> Signup and view all the answers

Which constraint helps to enforce business rules on data within a column?

<p>Check (A)</p> Signup and view all the answers

How do you add a column to an existing table using the ALTER TABLE command?

<p>Use the <code>ALTER TABLE</code> command followed by <code>ADD COLUMN</code>, specifying the column name, data type, and any constraints.</p> Signup and view all the answers

What is the purpose of the DROP CONSTRAINT clause in the ALTER TABLE command?

<p>To remove an existing constraint from a table.</p> Signup and view all the answers

Which DML command modifies existing data within a table?

<p>update (C)</p> Signup and view all the answers

Provide the syntax for the INSERT command to add a new row to a table named student.

<p>INSERT INTO student (column1, column2,...) VALUES (value1, value2,...);</p> Signup and view all the answers

What does the SELECT * FROM table_name command do?

<p>Retrieves all columns and rows from a table named <code>table_name</code>.</p> Signup and view all the answers

What is the purpose of the DISTINCT keyword in the SELECT command?

<p>To retrieve only unique values from a column.</p> Signup and view all the answers

Which operator is used to filter data based on a specific range of values (inclusive of both endpoints)?

<p>BETWEEN (C)</p> Signup and view all the answers

What is the purpose of the ORDER BY clause in the SELECT command?

<p>To sort the retrieved data in ascending or descending order.</p> Signup and view all the answers

What is the purpose of the TOP keyword in the SELECT command?

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

Which aggregate function calculates the average of all values in a column?

<p>AVG (B)</p> Signup and view all the answers

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Flashcards

Entity

A component of an ER diagram that represents a real-world object, such as a student or a course.

Attribute

A characteristic or property of an entity. For example, a student might have attributes like ID, name, and major.

Entity Instance

A specific instance of an entity. For example, a 'Student' entity might have instances like John Doe and Mary Smith.

Entity-Relationship Diagram (ERD)

Depicts the relationships between entities in a database. It helps in visualizing the structure of the data.

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Data Type

A specific type of data that can be stored in a column. Common database types include text, numbers, dates, and booleans.

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Conceptual ER Diagram

A visual representation of the relationships between entities, attributes, and their cardinality ratios in a database schema.

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Logical ER Diagram

A visual representation of the relationships between entities and attributes in a database schema, including primary and foreign keys.

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Key Attribute

A specific type of attribute that uniquely identifies each entity instance within its table.

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Composite Attribute

An attribute that is composed of multiple attributes. For example, an 'address' can be composed of 'street', 'city', and 'region'.

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Multi-value Attribute

A special type of attribute that can have multiple values for a single entity instance. For example, a 'hobbies' attribute could hold values like 'reading', 'sports', and 'music'.

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Complex Attribute

A more complex attribute that often contains sub-attributes. It is used to model data with multiple parts and complex structures, often associated with objects or collections with their own attributes.

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Derived Attribute

An attribute that is derived from other attributes in the same table. For example, 'age' can be derived from the 'birthdate' attribute.

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Binary Relationship

A relationship between two entities, represented by a diamond in an ERD, showing how they connect and interact.

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Cardinality Ratio

Describes the ratio of entity instances involved in a relationship. Examples include 1:1, 1:M, and M:N.

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Total Participation Constraint

A relationship where every entity instance on one side of the relationship must participate in the relationship.

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Partial Participation Constraint

A relationship where entity instances on one side of the relationship are not required to participate.

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Recursive Relationship

A relationship between an entity and itself. For example, an 'employee-supervisor' relationship where an employee can be both the supervisor and the supervisee.

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Ternary Relationship

A relationship involving three entities. For example, a 'Project-Employee-Department' relationship where an employee works on a project within a department.

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Strong Entity

An entity that exists independently and does not require another entity for its existence.

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Weak Entity

An entity that depends on another entity for its existence. A weak entity does not have its own primary key. Think of 'dependent' like a child needing a parent.

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Relational Schema Mapping

The process of converting a conceptual ERD into a relational schema, the blueprint of tables in a database.

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Relational Schema

The structure of tables in a database, including columns, data types, and relationships between tables.

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Primary Key

A column or set of columns that uniquely identifies each row in a table. It is used to ensure data integrity and prevent duplicate records. Choose them carefully as they are used for relationships between tables.

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Foreign Key

A column in one table that refers to the primary key in another table. Foreign keys are used to establish relationships between tables and ensure data consistency.

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Constraint

A set of rules that govern the data in a table, ensuring data integrity and consistency.

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Not Null Constraint

A constraint that ensures a column cannot contain NULL values, guaranteeing that the column always has a value.

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Check Constraint

A constraint that enforces a specific rule or condition on the data that can be stored in a column, ensuring that the data in the column meets specific criteria.

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Default Constraint

A constraint that automatically assigns a default value to a column if no value is provided during data entry, ensuring consistency and simplifying data input.

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Unique Constraint

A constraint that ensures that all values in a column are distinct and unique, preventing duplicate data and maintaining data integrity.

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Data Definition Language (DDL)

A language for managing the structure of the database. DDL commands create, modify, and delete tables and other database objects.

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Data Manipulation Language (DML)

SQL commands that manipulate data within the database. These commands are used to insert, delete, update, and retrieve data from tables.

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Select Command

A powerful command that retrieves data from tables. You can use various clauses to filter the data based on certain conditions and specific criteria.

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Insert Command

A DML command used to insert new rows of data into a table.

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Update Command

A DML command used to update existing data within a table.

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Delete Command

A DML command used to delete data from a table.

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Aggregate Functions

Functions that operate on a set of values, performing calculations and returning a single value. Common aggregate functions include SUM, AVG, COUNT, MAX, and MIN.

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Group By Clause

A clause used to group rows that have the same value in a specified column. It is often used in conjunction with aggregate functions for easier data analysis.

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Order By Clause

A clause allowing you to sort the data in an ascending or descending order.

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Study Notes

Database Design

  • Database design involves analysis, creating entity-relationship diagrams (ER diagrams), schema definition, and using DDL and DML.
  • Analysis is the first step, defining entities, attributes, and relationships.
  • Entities are objects, like students, instructors, courses.
  • Attributes are characteristics of entities, like student name, major, grade; instructor salary.
  • Relationships show how entities are connected, such as student-course (M:M), instructor-department (M:1), and course-section (1:M).

Attributes

  • Key attributes are unique identifiers (e.g., student ID, SSN).
  • Composite attributes are attributes with multiple parts (e.g., address includes street, city).
  • Multi-valued attributes have multiple values for an entity (e.g., phone numbers).
  • Derived attributes are calculated values based on other attributes (e.g., age from birthdate).

Relationships

  • Cardinality ratios describe the relationship between entities (e.g., 1:1, 1:M, M:M).
  • Participation constraints specify whether an entity is required in the relationship (e.g., total, partial).
  • Binary relationships connect two entities.
  • Recursive relationships occur when an entity is related back to itself (e.g., employee-supervisor).
  • Ternary relationships connect three entities (e.g., supplier, project, item).

Entity Types

  • Strong entities have their own unique identifiers.
  • Weak entities depend on a strong entity for their identifier (e.g., dependent, employee).

Converting ERD to Relational Schema

  • Entities become tables.
  • Attributes become columns.
  • Relationships become foreign keys linking tables.
  • A mapping algorithm converts ER models to relational tables.

SQL

  • SQL (Structured Query Language) is used to manipulate databases.
  • DDL (Data Definition Language) defines database structures (create, drop, alter).
  • DML (Data Manipulation Language) manipulates data (insert, update, delete, select).
  • Constraints are rules defining values.
  • Primary keys uniquely identify rows.
  • Foreign keys link tables using primary keys in other tables.
  • Constraints can include not null restrictions, uniqueness, check rules. Default values can also be defined.

Data Types

  • Data types define how data is stored (int, varchar, float).

DML Operations

  • Insert, update, and delete operations modify existing data.
  • Select retrieves data.

Queries and Constraints

  • SELECT statements retrieve data from tables.
  • Constraints ensure data accuracy and integrity.
  • Aggregate functions (count, sum, avg, min, max) calculate values across rows.
  • GROUP BY clause groups similar rows.

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