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

Remove duplicates without unique identifier: Netezza solution

In large Netezza tables, removing duplicate rows can be a difficult task without unique identifiers. While the provided SQL query may work in other databases, it fails in Netezza due to limitations of the DELETE clause after the WITH statement.

To overcome this challenge, we propose an alternative approach utilizing the USING keyword. The following Netezza query can remove duplicate rows seamlessly:

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 more AND conditions for other columns as needed ...

Here’s how it works:

• The USING keyword associates two tables T1 and T2, allowing us to perform a DELETE operation on T1 while referencing T2 to identify duplicates.
• Condition T1.ctid < T2.ctid ensures that only one of the duplicate rows is deleted.
• AND condition specifies the columns used to define duplicates.

You can see duplicates by replacing DELETE with SELECT * and USING with a comma (,) before executing DELETE:

SELECT * FROM table_with_dups T1, table_with_dups T2
WHERE T1.ctid < T2.ctid
  AND T1.column1 = T2.column1
  AND T1.column2 = T2.column2
  -- ... add more AND conditions for other columns as needed ...

All in all, this Netezza query provides an efficient solution for removing duplicate rows without a unique identifier, without the need for complex subqueries or window functions.

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