How to Pass Values from Python Code to PostgreSQL Queries

A comprehensive guide on successfully passing values from Python to PostgreSQL queries while avoiding SQL injection.
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How to Pass Values from Python Code to PostgreSQL Queries

When working with Python, especially when handling data from sources such as Excel, it's common to want to store that data in a database like PostgreSQL. In this guide, we will address a problem commonly faced by developers: how to pass values from Python to a PostgreSQL query correctly.

The Problem: Error in Passing Values to PostgreSQL

You may find yourself reading data into a pandas DataFrame, then attempting to insert that data into a PostgreSQL database via a function call. However, you might encounter errors like the following:

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

The reason for this error can often be traced back to how arguments are being passed to the database function or procedure. To illustrate the problem, consider this code snippet:

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

While it may seem correct, it fails due to type mismatches or function definition discrepancies. On the other hand, you might find that using an f-string seems to work at first glance but opens yourself up to SQL injection vulnerabilities.

Solution Steps: How to Fix Value Passing Issues

1. Understanding Function and Procedure Calls

First, it's essential to comprehend the differences between calling a function and calling a procedure in PostgreSQL:

Function Call: Uses SELECT to retrieve results.

Procedure Call: Uses CALL to execute procedures that do not return a value directly.

2. Use Functions Correctly

If you're trying to get a result back from the controldubbel2 function, use the following format:

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

Alternatively, to avoid SQL injection risks while using CALL for procedures, your code should look like this:

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

3. Ensure Correct Data Types

When passing values to procedures or functions, ensure that the saved variables in Python have matching data types consistent with those in your PostgreSQL function definition. This helps mitigate errors such as:

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4. Example of Correct Implementation

For example, if you have a PostgreSQL function like below:

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

When you want to call it from Python, do the following:

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

This code structure will help you pass the values correctly while keeping the data safe from SQL injections.

Conclusion

In summary, passing values from Python to PostgreSQL queries involves understanding function and procedure usage, maintaining data type consistency, and formatting your queries appropriately. Following these structured practices will not only solve your immediate issues but also enhance your application's security and performance.

With this guidance, you should be able to navigate these challenges more effectively. Happy coding!