Databases：练习题

In the context of a relational database, which term is used to describe a single record within a table?

A database table is considered to be in First Normal Form (1NF) if it satisfies which of the following criteria?

In a relational database where referential integrity is enforced, what is the default behavior when a user attempts to delete a record in a parent table that has related records in a child table?

A database administrator is evaluating the efficiency of a relational database. To improve the speed of data retrieval for a specific attribute without altering the logical schema or the physical storage order of the records, which database feature should be implemented?

A database table for OrderDetails contains the following attributes: (OrderID, ProductID, ProductName, UnitPrice, Quantity).

The combination (OrderID, ProductID) serves as the primary key. If ProductName depends only on ProductID, which of the following statements accurately describes the current state of this table?

In the context of a relational database, state the term used to describe a field in one table that refers to the primary key in another table, used to establish a relationship between the two tables.

Explain why a many-to-many relationship between two entities, such as STUDENT and COURSE, cannot be directly implemented in a relational database and state how this is resolved.

In the context of a Database Management System (DBMS), describe the role of the data dictionary in maintaining data integrity and explain how the query processor interacts with it during the execution of a DML statement.

A small library currently stores its book information in a simple text file. Each line in the file contains the book's title, author, ISBN, and availability status (e.g., 'Title, Author, ISBN, Available').

(a) State two limitations of using this file-based approach for managing library data.

(b) Explain how a relational database system addresses one of the limitations you identified in part (a).

A company maintains a database of its projects and the employees assigned to them. The current data is stored in a single table called ProjectAssignments:

The primary key for this table is a composite key: (ProjectID, EmployeeID).

(a) Explain why the ProjectAssignments table is not in Second Normal Form (2NF).

(b) Decompose the ProjectAssignments table into tables that are in Second Normal Form (2NF), clearly stating the primary key(s) and any foreign key(s) for each new table.