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A comprehensive guide on removing duplicates from your Oracle SQL table, ensuring data integrity with easy-to-follow SQL commands.
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How to Delete Duplicates from a Table in Oracle SQL

When working with databases, maintaining clean and accurate data is essential. One common issue that arises is having duplicate entries in a table. This can lead to confusion during data retrieval and analysis. In this guide, we will explore how to effectively delete duplicates from a given table in Oracle SQL, using a clear example to illustrate the process.

Introduction to the Problem

Consider a scenario in which you have a table named TABLE1 in your Oracle database. This table has several columns, and you’ve noticed that it contains a significant number of duplicate records. Below is the schema for TABLE1:

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Now, let’s say you have inserted several records into this table, and you’re facing the following issue:

You have nearly 400 duplicate rows across the table.

For each unique PAN_ID that appears more than once, you want to delete all but one of these duplicates.

Sample Data

Here are some sample entries to illustrate the duplicate issue:

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As observed, A1, B1, and C1 are repeated, leading to a cluttered dataset.

The Solution

To resolve the issue of duplicate rows in TABLE1, you can execute an effective DELETE statement. The goal is to keep only one instance of each PAN_ID. You can achieve this with the following SQL command:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the SQL Command

DELETE Statement: This command specifies that you wish to delete records from TABLE1.

WHERE Condition: The condition checks if the ROWID of the current record (T1) is greater than the minimum ROWID found for the same PAN_ID in the table (T2).

Subquery: The subquery identifies the ROWID of the first occurrence of each PAN_ID within TABLE1. This means that for each duplicate, only the one with the smallest ROWID will remain.

Execution Steps

Open your SQL Developer application.

Copy and paste the DELETE command provided above.

Execute the command to remove duplicates.

Conclusion

By utilizing the above SQL command, you can effectively clean your TABLE1 by removing duplicate entries while retaining one instance of each PAN_ID. This approach ensures data integrity and accuracy in your database operations.

If you often face issues with duplicates in your database, consider implementing checks and constraints during data insertion to prevent such issues from occurring in the first place. Keeping your database clean is crucial for efficient data handling and retrieval.

Feel free to follow up with any questions or experiences you may have had regarding handling duplicates in Oracle SQL!