How to Create a Set-Returning PostgreSQL Function for Multiple Records

Описание: Discover how to create a PostgreSQL function that returns multiple records from each table in a specified schema. Get step-by-step guidance and best practices.
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This video is based on the question https://stackoverflow.com/q/63755928/ asked by the user 'A gupta' ( https://stackoverflow.com/u/11901224/ ) and on the answer https://stackoverflow.com/a/63757260/ provided by the user 'Игорь Тыра' ( https://stackoverflow.com/u/12081543/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Mastering PostgreSQL Functions: Returning Multiple Records from a Table

When working with PostgreSQL, many users find themselves needing to execute functions across various tables within a specific schema. If you're new to PostgreSQL functions, you might come across issues, especially when it comes to retrieving multiple records from a single function call. In this guide, we'll explore a common challenge when trying to return multiple records from every table in a PostgreSQL schema and provide a clear solution to this problem.

The Challenge

Imagine you have a function set to run for every table in a schema, but your function only returns a single record each time it is called. This can be limiting and problematic, especially if you need to retrieve n number of records from each table. Here, we'll look at a code snippet to showcase this issue:

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

In this setup, the main issue is that the function is returning just one record thanks to the execute ... into result syntax. But fear not! There is a better way to design this function.

The Solution: Creating a Set-Returning Function

To resolve the above limitations, you'll need to modify your existing function to return a set of records. This allows the function to handle multiple records from the database tables effectively. Here’s how you can do it:

Step-by-Step Implementation

Change the Return Type: Modify the function to return a SETOF text, which indicates that it can return multiple rows.

Format the SQL Query Properly: Using the FORMAT function will help prevent SQL injection and make your code cleaner.

Return the Query Result: Utilize RETURN QUERY EXECUTE to execute the query and return all records at once.

Here is the corrected function:

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

Explanation of Changes

RETURNS SETOF text: This change allows the function to return multiple results instead of just a single one.

FORMAT() Function: This is a best practice in PostgreSQL to safely format your SQL queries. It guards against possible SQL injection attacks, while also making the code more readable.

RETURN QUERY EXECUTE _query: Instead of fetching a single record, this line executes the query and returns all matching rows as a set.

Conclusion

By creating a set-returning function in PostgreSQL, you empower your application to handle datasets efficiently and effectively. No longer will you be restricted to processing just one record at a time! This method not only enhances your PostgreSQL function capabilities but also ensures you follow best practices in SQL coding.

If you run into any setbacks while implementing this solution, feel free to reach out for further help. Happy querying!