Detect and Eliminate Update Anomalies in SQL

Identifying and Resolving Update Anomalies

Write a SQL query to identify and resolve update anomalies in a poorly designed table.

Solution:

-- Poorly designed table with update anomalies.
CREATE TABLE Students (
    StudentID INT,
    CourseID INT,
    CourseName VARCHAR(100),
    InstructorName VARCHAR(100)
);

-- Resolve anomalies by normalizing into three tables.
CREATE TABLE Courses (
    CourseID INT PRIMARY KEY,
    CourseName VARCHAR(100)
);

CREATE TABLE Instructors (
    InstructorID INT PRIMARY KEY,
    InstructorName VARCHAR(100)
);

CREATE TABLE StudentCourses (
    StudentID INT,
    CourseID INT,
    InstructorID INT,
    PRIMARY KEY (StudentID, CourseID),
    FOREIGN KEY (CourseID) REFERENCES Courses(CourseID),
    FOREIGN KEY (InstructorID) REFERENCES Instructors(InstructorID)
);

Explanation:

• Purpose of the Query :
• The goal is to identify update anomalies and resolve them through normalization.
• Key Components :
• Courses and Instructors: Store course and instructor details independently.
• StudentCourses: Links students to courses and instructors.
• Why Resolve Anomalies? :
• Update anomalies occur when changes to one attribute require updates in multiple rows.
• Normalization ensures consistency and reduces maintenance effort.
• Real-World Application :
• In school databases, normalization avoids inconsistencies in course and instructor data.

Notes:

• Update anomalies are common in denormalized tables.
• Use normalization to simplify updates and reduce errors.
• Important Considerations:
• Balance normalization with query performance.

For more Practice: Solve these Related Problems:

• Write a SQL query to identify update anomalies in a table where customer details and order details are stored together and resolve them through normalization.
• Write a SQL query to redesign a table storing employee roles and department details to avoid update anomalies.
• Write a SQL query to normalize a table containing product inventory and supplier details to eliminate update anomalies.
• Write a SQL query to resolve update anomalies in a table where course details and instructor details are combined.

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous SQL Exercise: Achieving Boyce-Codd Normal Form (BCNF).
Next SQL Exercise: Designing a Junction Table for Many-to-Many Relationships.