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':

<code class="language-sql">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</code>

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:

<code class="language-sql">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</code>

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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