Writing Database Queries to Resolve Data Duplication and Inconsistency Issues

Understanding Data Duplication Issues and Analyzing Causes

There is a problem of duplicate results occurring when querying data from the database. To resolve this issue, it is essential to understand the root causes accurately. The problematic query is as follows:

SELECT * FROM ARTICLE
ORDER BY posted DESC
LIMIT 10, 10

Identifying the Cause of the Issue

Duplicate data issues primarily arise when the 'posted' column has duplicate values. The database sorts based on the 'posted' value alone, and it does not guarantee a specific order for identical values. Consequently, when using the 'LIMIT' clause to retrieve the next page, duplicate results may appear.

Solution to Data Duplication Problem

To address this issue, it is necessary to add an additional sorting criterion for data with identical 'posted' values to ensure consistent order. For this purpose, the 'id' column can be used as an additional sorting criterion. The modified query is as follows:

SELECT * FROM ARTICLE
ORDER BY posted DESC, id DESC
LIMIT 10, 10

Using this approach, the query first sorts by the 'posted' column and then adds sorting by the 'id' column for records with the same 'posted' value, eliminating duplicate results. This ensures that the result pages do not overlap, providing consistent outcomes.

Additionally, in databases like SQLite, you can apply an additional sorting criterion using a unique identifier called 'ROWID.' Information regarding this can be found in the SQLite official documentation.

SELECT * FROM ARTICLE
ORDER BY posted DESC, ROWID DESC
LIMIT 10, 10

Summary

When composing queries, adding a unique sorting criterion for identical 'posted' values can resolve data duplication issues. This ensures the smooth functioning of pagination features.