How do I eliminate SQL duplicates?

SQL Programming Training Expert on Eliminating Duplicates

Introduction

As a seasoned tutor specializing in SQL Programming Training with a strong presence on UrbanPro.com, I understand the importance of addressing common challenges faced by learners. One such frequent query involves eliminating duplicates in SQL, a fundamental skill in database management.

Understanding the Issue

When working with databases, encountering duplicate records is commonplace. These duplicates can distort data accuracy and create inefficiencies. To tackle this problem, individuals often seek guidance on how to eliminate duplicates effectively.

Strategies for Eliminating SQL Duplicates

1. Use DISTINCT Keyword

• Explanation: The DISTINCT keyword is a simple yet powerful tool to eliminate duplicate rows from a result set.
• Example:
  sql

• SELECT DISTINCT column1, column2 FROM your_table;

2. GROUP BY Clause

• Explanation: GROUP BY groups rows that have the same values into summary rows, allowing you to identify and eliminate duplicates.
• Example:
  sql

• SELECT column1, column2, COUNT(*) FROM your_table GROUP BY column1, column2 HAVING COUNT(*) > 1;

3. Using ROW_NUMBER()

• Explanation: This approach assigns a unique number to each row, making it easy to identify and remove duplicates.
• Example:
  sql

• WITH CTE AS ( SELECT column1, column2, ROW_NUMBER() OVER (PARTITION BY column1, column2 ORDER BY column1) AS RowNum FROM your_table ) DELETE FROM CTE WHERE RowNum > 1;

4. Self-Joins

• Explanation: Self-joins can be employed to compare rows within the same table and eliminate duplicates based on specified conditions.
• Example:
  sql