How to Delete Duplicate Rows in NetezzaSQL Without a Unique Identifier?

Removing Duplicate Rows in Netezza SQL: A Practical Guide

Netezza SQL doesn't directly support the standard WITH clause approach for deleting duplicate rows. However, a robust alternative uses the USING keyword. This method effectively eliminates duplicates without relying on a unique identifier.

The following query demonstrates how to delete duplicate entries from a table named 'table_with_dups':

DELETE FROM table_with_dups T1
USING table_with_dups T2
WHERE T1.ctid < T2.ctid AND T1.column1 = T2.column1 AND T1.column2 = T2.column2; --Add all relevant columns here

Important Note: Replace column1, column2, etc. with the actual column names in your table that define a duplicate row. You must include all columns that contribute to the definition of a duplicate.

This query compares rows based on their ctid (system-generated unique row identifier) and the specified columns. It deletes the row with the smaller ctid for each duplicate set.

Pre-Deletion Verification:

Before executing the DELETE statement, it's crucial to verify the rows slated for deletion. Run this query to preview the affected records:

SELECT * FROM table_with_dups T1
USING table_with_dups T2
WHERE T1.ctid < T2.ctid AND T1.column1 = T2.column1 AND T1.column2 = T2.column2; --Add all relevant columns here

This SELECT statement mirrors the DELETE query, allowing you to inspect the data before making any permanent changes. This precautionary step is highly recommended to avoid unintended data loss.

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