Finding duplicate values in an Oracle database table is a standard data cleanup and validation requirement. Here’s the most straightforward SQL statement to retrieve duplicates and their occurrence counts.

SQL Query to Find Duplicate Values

Use the following query to identify duplicate values in a specified column of an Oracle table:

SELECT table_field, COUNT(table_field) AS dup_count
FROM table_name
GROUP BY table_field
HAVING (COUNT(table_field) > 1);

How It Works

1. SELECT table_field: This retrieves the column you want to check for duplicates.
2. COUNT(table_field): This calculates the number of occurrences for each value.
3. GROUP BY table_field: This groups the rows by the unique values in the specified column.
4. HAVING (COUNT(table_field) > 1): This filters out groups with only one occurrence, showing only duplicates.

Example Output

Let’s say you have a table called employees with a column department_id. Running the query:

SELECT department_id, COUNT(department_id) AS dup_count
FROM employees
GROUP BY department_id
HAVING (COUNT(department_id) > 1);

Would result in:

This indicates that department_id 101 appears 3 times, and department_id 202 appears 2 times.

Additional Tips

• Replace table_field and table_name with the actual column and table names from your database.
• To find duplicates across multiple columns, include them all in the GROUP BY clause.
• Always test your query in a development environment before using it in production.

Finding duplicates can help identify inconsistencies, improve data quality, and streamline database operations. Would you like to explore more advanced SQL techniques? 😊

Ahmad Gohar

With over 18 years of experience in software architecture, Java technologies, and leadership, I specialize in crafting scalable, future-proof solutions for global organizations. Whether it’s transforming legacy systems, building cutting-edge cloud-native applications, or mentoring teams to excel, I’m committed to delivering value-driven results.

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