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Questions and Answers
A derived attribute is stored directly in the database.
A derived attribute is stored directly in the database.
False
Derived attributes are included in the relational schema.
Derived attributes are included in the relational schema.
False
Derived attributes can help in reducing redundancy by not being stored.
Derived attributes can help in reducing redundancy by not being stored.
True
The value of a derived attribute can change based on changes in the other attributes it depends on.
The value of a derived attribute can change based on changes in the other attributes it depends on.
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Derived attributes are often used to simplify queries in a database.
Derived attributes are often used to simplify queries in a database.
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A composite attribute can consist of more than one attribute which is considered a candidate key.
A composite attribute can consist of more than one attribute which is considered a candidate key.
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Multi-value attributes should be included in the same table as their parent attributes without any modification.
Multi-value attributes should be included in the same table as their parent attributes without any modification.
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When dealing with multi-value attributes, foreign keys are introduced in the new table created.
When dealing with multi-value attributes, foreign keys are introduced in the new table created.
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Each attribute within a composite attribute is treated as an independent entity.
Each attribute within a composite attribute is treated as an independent entity.
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Creating a new table for multi-value attributes is a step towards database normalization.
Creating a new table for multi-value attributes is a step towards database normalization.
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A Not Null Constraint allows a column to contain NULL values.
A Not Null Constraint allows a column to contain NULL values.
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Not Null Constraint is used to ensure that data is always present in a specified column.
Not Null Constraint is used to ensure that data is always present in a specified column.
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Adding a Not Null Constraint to a column will allow NULL values if existing entries already include them.
Adding a Not Null Constraint to a column will allow NULL values if existing entries already include them.
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The Not Null Constraint can be applied to multiple columns at once.
The Not Null Constraint can be applied to multiple columns at once.
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A Not Null Constraint is optional and not necessary for database integrity.
A Not Null Constraint is optional and not necessary for database integrity.
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A table can have multiple primary key constraints.
A table can have multiple primary key constraints.
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The primary key constraint is created using the primary key keyword.
The primary key constraint is created using the primary key keyword.
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The foreign key constraint allows data in a column to be unique across all tables.
The foreign key constraint allows data in a column to be unique across all tables.
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Data entered in a column with a foreign key constraint can exist independently of other tables.
Data entered in a column with a foreign key constraint can exist independently of other tables.
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A foreign key constraint is unnecessary if the data in the column does not need to relate to another table.
A foreign key constraint is unnecessary if the data in the column does not need to relate to another table.
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The command to remove a constraint from a table is written as DELETE CONSTRAINT ...
The command to remove a constraint from a table is written as DELETE CONSTRAINT ...
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To drop a constraint from the employee table, the command would be ALTER TABLE employee DROP CONSTRAINT employee_age.
To drop a constraint from the employee table, the command would be ALTER TABLE employee DROP CONSTRAINT employee_age.
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Constraints must be dropped using the command REMOVE CONSTRAINT ....
Constraints must be dropped using the command REMOVE CONSTRAINT ....
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The example code provided shows how to drop a constraint named city_default from the person table.
The example code provided shows how to drop a constraint named city_default from the person table.
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The syntax for dropping a constraint does not require the name of the constraint to be specified.
The syntax for dropping a constraint does not require the name of the constraint to be specified.
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The SQL command 'SELECT * FROM student WHERE GPA IN (90, 85, 75, 60);' retrieves records with GPA values of 90, 85, 75, or 60.
The SQL command 'SELECT * FROM student WHERE GPA IN (90, 85, 75, 60);' retrieves records with GPA values of 90, 85, 75, or 60.
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The command 'SELECT * FROM student WHERE GPA BETWEEN 60 AND 90;' will exclude GPAs of 60 and 90.
The command 'SELECT * FROM student WHERE GPA BETWEEN 60 AND 90;' will exclude GPAs of 60 and 90.
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Using 'SELECT DISTINCT GPA FROM student;' will return a list of unique GPA values from the student table.
Using 'SELECT DISTINCT GPA FROM student;' will return a list of unique GPA values from the student table.
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The clause 'WHERE GPA < 75' will filter results to only return students with GPAs less than 75.
The clause 'WHERE GPA < 75' will filter results to only return students with GPAs less than 75.
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The SQL command 'SELECT COUNT(*) FROM student;' retrieves the average GPA of all students in the table.
The SQL command 'SELECT COUNT(*) FROM student;' retrieves the average GPA of all students in the table.
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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 is the initial step.
- Attributes are characteristics of entities.
- Relationships define connections between entities (e.g., 1:1, 1:M, M:M). Examples of relationships include student-course (M:M), course-section (1:M), department-course (1:M), and instructor-department (M:1).
Attributes
- Key attributes are unique identifiers (e.g., ID, SSN).
- Composite attributes are formed from multiple parts (e.g., address).
- Single valued attributes have only one value for an entity (e.g., name).
- Multivalue attributes can take multiple values (e.g., phone numbers).
- Derived attributes are calculated from other attributes (e.g., age from birthdate).
Entities
- Strong entities have their own unique identifier (e.g., student).
- Weak entities depend on a strong entity for their unique identifier (e.g., dependent). A weak entity has attributes that need the ID of the strong entity to be uniquely identified.
Relationships
- Binary relationships connect two entities.
- Recursive relationships relate an entity to itself (e.g., employee-supervisor).
- Ternary relationships involve three entities (e.g., supplier-project-item).
Cardinality Ratio (Relationships)
- Cardinality ratio describes the numerical relationship between entities (1:1, 1:M, M:M).
- Participation constraints specify whether an entity is optional or mandatory in a relationship (total participation, partial participation).
Schema
- Schema defines the structure of the database.
- It includes the names of tables(relations) and attributes, data types, and constraints.
Mapping Algorithms (ERD to relational schema)
- Mapping algorithms are tools to design the schema from the ER diagram.
- Mapping algorithms are used to convert from an ER Diagram to a relational schema.
Database Management System (DBMS)
- DBMS manages database operations (e.g., data storage, retrieval). Examples of DBMS include SQL Server.
SQL
- SQL is a structured query language used to manage and manipulate data in a relational database.
- SQL commands include CREATE, DROP, ALTER (DDL), INSERT, UPDATE, DELETE (DML), SELECT, and others.
Constraints in SQL
- Constraints (e.g., not null, unique, check, default, primary key, foreign key) help enforce data integrity.
- primary keys uniquely identify tuples within a table
- constraints for integrity and enforce data integrity.
- data type: examples of data types include int for integer values, varchar(10) as strings limited to 10 characters, float to hold floating-point values, and so on.
- the constraint 'not null' prevents a field from having a missing value.
- the constraint 'unique' prevents the same value from being repeated in a field.
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Description
Test your understanding of derived and composite attributes in databases, as well as the concepts of multi-value attributes and constraints like Not Null. This quiz covers key principles of database normalization and design, ensuring that you grasp their significance in maintaining data integrity and efficiency.
