Eliminating Deletion Anomalies with Proper Database Normalization

Resolving Deletion Anomalies in Database Design

Write a SQL query to resolve deletion anomalies in a poorly designed table.

Solution:

-- Poorly designed table with deletion anomalies.
CREATE TABLE Departments (
    DepartmentID INT PRIMARY KEY,
    DepartmentName VARCHAR(100),
    ManagerID INT,
    ManagerName VARCHAR(100)
);

-- Resolve deletion anomalies by separating manager details.
CREATE TABLE Managers (
    ManagerID INT PRIMARY KEY,
    ManagerName VARCHAR(100)
);

CREATE TABLE Departments_Normalized (
    DepartmentID INT PRIMARY KEY,
    DepartmentName VARCHAR(100),
    ManagerID INT,
    FOREIGN KEY (ManagerID) REFERENCES Managers(ManagerID)
);

Explanation:

• Purpose of the Query :
• The goal is to resolve deletion anomalies by separating related attributes into their own tables.
• Key Components :
• Managers: Stores manager details independently.
• Departments_Normalized: Links departments to managers via a foreign key.
• Why Resolve Deletion Anomalies? :
• Deletion anomalies occur when deleting one record unintentionally removes related data.
• Normalization ensures that deleting a department does not delete manager information.
• Real-World Application :
• In organizational databases, normalization avoids issues when reassigning or removing departments.

Notes:

• Deletion anomalies are common in denormalized tables.
• Use normalization to simplify data maintenance and avoid unintended data loss.
• Important Considerations:
• Ensure referential integrity when splitting tables.

For more Practice: Solve these Related Problems:

• Write a SQL query to redesign a table storing project details and team members to avoid deletion anomalies when a project is removed.
• Write a SQL query to normalize a table containing course details and instructor information to prevent data loss when a course is deleted.
• Write a SQL query to split a table storing department and employee details into separate tables to avoid accidental deletion of employee records.
• Write a SQL query to resolve deletion anomalies in a table where supplier and product details are combined.

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