Скачать или смотреть Resolving the Postgres Upsert Cardinality Violation Error

Learn how to handle `Postgres Upsert Cardinality Violation` errors when inserting data into PostgreSQL tables with conflicts. This guide provides a clear solution and best practices for effective data management.
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Resolving the Postgres Upsert Cardinality Violation Error

When working with databases, encountering errors can be frustrating, especially when they're related to data insertion and integrity. One common issue that developers face in PostgreSQL is the Cardinality Violation error during an upsert operation. This post aims to shed light on this error and provide practical solutions to overcome it.

Understanding the Problem

Suppose you have a PostgreSQL table defined as follows:

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You want to insert multiple rows into this table. If a row with a matching job_id already exists, rather than causing an error or rejecting the entry, you want to update that row, specifically setting the complete column back to its default value (which is 0).

Your SQL query looks something like this:

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However, when running this query, you encounter the following error:

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This error indicates that the insert operation is attempting to modify the same row more than once due to duplicate job_id values in your input data.

Breaking Down the Error

Why Does This Error Occur?

Duplicate job_id Values: The most common cause of this error is an attempt to insert multiple rows where two or more rows contain the same job_id. When PostgreSQL attempts the ON CONFLICT DO UPDATE operation, it cannot apply the update to the same row multiple times in a single query.

How to Resolve It

To effectively handle this error, ensure that your insertion data does not contain any duplicate job_id values. Here’s how you can do that:

Check Input Data: Before performing your insert operation, verify that your {jobs_sql} variable (which contains the rows you plan to insert) does not include duplicate job_id values. Implement checks in your data extraction or preprocessing phase to eliminate duplicates.

Use a Temporary Table: If eliminating duplicates directly is difficult, a possible workaround is to first insert data into a temporary table that allows duplicates, and then apply the unique values to the target table.

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Conclusion

Dealing with Postgres Upsert Cardinality Violation errors can be challenging, but with a bit of preparation and understanding, you can easily overcome these obstacles. Always be vigilant about the data integrity in your input and ensure that no duplicate job_id values exist when executing an upsert operation. By following these best practices, you can maintain smooth and error-free database operations.

If you continue to face challenges or have any further questions, feel free to reach out!