How to Efficiently Delete Duplicate Rows in an SQLite Database?

Identifying and Removing Duplicate Rows in SQLite Database

Duplication within database records can arise, posing a challenge when maintaining data integrity and optimizing performance. This scenario involves a large SQLite3 table with two columns, 'hash' (text) and 'd' (real), where some rows exhibit duplicate values for both columns. The objective is to efficiently delete these duplicate rows while preserving the unique rows.

The provided solution utilizes the unique rowid column in SQLite to distinguish rows. The query below targets and eliminates duplicate rows by retaining the lowest rowid value for each unique combination of 'hash' and 'd' values:

delete   from YourTable
where    rowid not in
         (
         select  min(rowid)
         from    YourTable
         group by
                 hash
         ,       d
         )

This query operates by first identifying the minimum rowid for each distinct combination of 'hash' and 'd' values through a subquery. The 'min(rowid)' function extracts the lowest rowid for each group of identical 'hash' and 'd' pairs. Subsequently, the main query utilizes the 'rowid not in' clause to delete any rows whose rowid does not correspond to the minimum rowid for their respective 'hash' and 'd' values.

By leveraging this approach, the query efficiently identifies and removes duplicate rows while preserving the unique data within the table. The utilization of the rowid column as a unique identifier facilitates a rapid and effective deletion process, ensuring data accuracy and optimizing database performance for future operations.

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