Скачать или смотреть How to Insert Values into a PostgreSQL Table with Psycopg2 using a Where Conditional

Learn how to effectively insert values from one PostgreSQL table into another using Psycopg2, incorporating a WHERE condition for selection.
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How to Insert Values into a PostgreSQL Table with Psycopg2 using a Where Conditional

Are you new to PostgreSQL or Psycopg2 and struggling with inserting values into a table based on conditions from other tables? You’re not alone! Many beginners face challenges when trying to perform more complex SQL operations like this. In this post, we’ll take a closer look at a common scenario: inserting values from one table into another with the help of Psycopg2 while applying a WHERE condition.

The Problem

You might encounter situations where you want to populate a new table with values derived from existing tables. In this case, you want to insert two columns into TABLE_ONE, using values from TABLE_TWO and TABLE_THREE, conditioned by specific criteria. Let’s take a look at the code that’s causing issues:

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

When trying to execute this code, you receive an error related to a NotNullViolation, implying that the values being inserted are null. This indicates that something is going wrong in the value selection process.

Analyzing the Issue

It seems your error might be due to a mix-up in the order of the elements within the insert_values variable. The values supplied should match the order in which they are used in the SQL query. If they do not match, the database will receive null where it expects valid data, thus violating any NOT NULL constraints in the target table.

Common Errors

NotNullViolation: This happens when you attempt to insert a null value into a column that does not allow it.

Incorrect Value Order: Mismatches where the values are expected versus where they are provided can lead to misleading errors.

The Solution

To resolve this issue, you need to ensure that the values you are extracting and providing in the insert_values tuple correctly correspond to the expected columns in the SQL statement.

Steps to Fix the Issue

Check Column Names and Order: Verify that LT_ID_ONE corresponds to the first placeholder in your SQL string, and LT_ID_TWO corresponds to the second placeholder.

Update the insert_values Tuple: Adjust the order of your values being passed into insert_values.

Here is the corrected code snippet:

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

Final Thoughts

By swapping the elements in the insert_values tuple, you should be able to insert the correct values into TABLE_ONE without encountering NotNullViolation errors. Always ensure that the values you derive from other tables align properly with those expected by the target table.

Happy coding! If you have any further questions or run into any other errors, feel free to reach out.