Скачать или смотреть Using psycopg2 to Copy Data Between PostgreSQL Schemas

Struggling to copy data between schemas in PostgreSQL using `psycopg2`? This guide provides a clear and step-by-step solution to help you avoid common pitfalls and successfully transfer your data.
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This video is based on the question https://stackoverflow.com/q/68710913/ asked by the user 'Viktor Andriichuk' ( https://stackoverflow.com/u/8118448/ ) and on the answer https://stackoverflow.com/a/68715073/ provided by the user 'Adrian Klaver' ( https://stackoverflow.com/u/7070613/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Overcoming Issues When Copying Data Between PostgreSQL Schemas

Transferring data between schemas in PostgreSQL can be a straightforward task when done correctly. However, it can quickly turn into a headache if things are not executed properly. In this guide, we will address a common issue encountered while using psycopg2 for copying data from one schema to another and provide a step-by-step solution to overcome it. Let's dive in!

The Problem

Recently, a user encountered an error while attempting to copy data from a public schema to a target schema using the following SQL command in psycopg2:

[[See Video to Reveal this Text or Code Snippet]]

The error message the user received was:

[[See Video to Reveal this Text or Code Snippet]]

This error indicates that the query is incorrectly trying to insert a record instead of the individual column values, leading to mismatches with the column types defined in the target schema.

Understanding the Solution

To resolve this issue, a few changes need to be made to ensure that the INSERT statement is formed correctly. It is essential to capture the columns in the correct format and to specify which columns you want to insert into explicitly. Below are the steps to fix the problem.

1. Fixing the SQL Query Structure

The initial issue lies in how the SELECT part of the query is structured. Instead of enclosing the column names in parentheses, they should be selected individually without parentheses. Here’s how:

Incorrect Structure:

[[See Video to Reveal this Text or Code Snippet]]

This treats the selected columns as a single record, leading to the type mismatch error.

Correct Structure:

[[See Video to Reveal this Text or Code Snippet]]

2. Constructing the Correct INSERT Statement

Next, the INSERT statement should specify the columns explicitly where the data will be inserted. Here’s what the corrected SQL command should look like:

[[See Video to Reveal this Text or Code Snippet]]

3. Final Working Example

Here’s how the complete sequence of commands would look when executed correctly:

[[See Video to Reveal this Text or Code Snippet]]

Executing the final command will successfully copy the data from the public schema to the target schema.

Conclusion

Copying data between schemas in PostgreSQL using psycopg2 can be error-prone if SQL queries are not structured correctly. By ensuring that you select the individual columns without grouping them into a record and specifying the columns directly in your INSERT statement, you can successfully copy your data without running into type errors.

If you encounter further issues or have questions, feel free to reach out, and happy coding!