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How to Convert Select Row_number Query to Delete Query on Postgresql?

3 minutes read

To convert a SELECT query with row_number to a DELETE query in PostgreSQL, you can use a Common Table Expression (CTE) to first select the rows you want to delete and then use the DELETE statement with a WHERE clause that filters based on the row numbers generated in the CTE. This allows you to delete specific rows based on their row numbers without having to explicitly list them in the DELETE statement. By using window functions like ROW_NUMBER() in the CTE, you can assign row numbers to the rows in the result set and then delete the rows that meet your criteria.


What is the recommended approach for deleting rows using row_number in PostgreSQL?

One recommended approach for deleting rows using row_number in PostgreSQL is to first identify the rows that you want to delete using a subquery with the row_number() window function. You can then use a delete statement with a where clause that filters out the rows based on their row_number values.


Here is an example of deleting rows with a row_number condition:

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WITH numbered_rows AS (
  SELECT *,
         ROW_NUMBER() OVER (ORDER BY column_name) AS row_num
  FROM your_table
)
DELETE FROM your_table
WHERE primary_key IN (
  SELECT primary_key
  FROM numbered_rows
  WHERE row_num BETWEEN start_row_num AND end_row_num
);


In this example, the rows are first assigned row numbers using the row_number() window function. The delete statement then filters out the rows based on their row numbers.


It's important to note that the primary_key column should be used as a reference for deleting rows, as it uniquely identifies each row in the table. Make sure to adjust the column_name, your_table, primary_key, start_row_num, and end_row_num to match your specific use case.


How to delete rows based on row_number in PostgreSQL?

To delete rows based on row_number in PostgreSQL, you can use a subquery with the ROW_NUMBER() window function to add row numbers to each row and then use a DELETE statement with a WHERE clause that specifies the row_number condition.


Here is an example query that deletes rows based on row_number in PostgreSQL:

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DELETE FROM your_table
WHERE row_number IN (
    SELECT row_number
    FROM (
        SELECT row_number() OVER () as row_number
        FROM your_table
    ) subquery
    WHERE condition_to_select_rows_to_delete
);


In the above query:

  • Replace "your_table" with the name of your table.
  • Adjust "condition_to_select_rows_to_delete" with the specific condition that you want to use to select the rows to be deleted based on their row_number.


Make sure to backup your data before running the DELETE statement to avoid accidentally deleting important data.


What is the limitation of using row_number for deletion in PostgreSQL?

One limitation of using the row_number function for deletion in PostgreSQL is that it requires the retrieval of all rows in the table in order to assign row numbers before deleting. This can be inefficient and resource-intensive, especially for large tables with millions of rows. Additionally, if the table is being actively updated or has concurrent transactions, using row_number for deletion can lead to potential race conditions and inconsistencies in the data.

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