Solving the Vertica Column Drop Dilemma скачать в хорошем качестве

Solving the Vertica Column Drop Dilemma

Discover how to successfully drop a column in `Vertica` without losing your entire table. Follow our detailed, easy-to-understand solution layout to navigate common issues. --- This video is based on the question https://stackoverflow.com/q/70323265/ asked by the user 'Manu Chadha' ( https://stackoverflow.com/u/6703783/ ) and on the answer https://stackoverflow.com/a/70324752/ provided by the user 'marcothesane' ( https://stackoverflow.com/u/6788255/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Why am I not able to drop a column in Vertica Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l... The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- Solving the Vertica Column Drop Dilemma: A Step-by-Step Guide When working with databases, especially with systems like Vertica, you may find yourself wanting to make adjustments to your table structures. One common task is the deletion of columns. But what happens when an attempt to drop a column results in an error? If you've encountered the issue where you can't drop a column in Vertica, you're not alone. In this post, we'll explore why this happens and provide a clear, step-by-step solution. The Problem: Unable to Drop the Column Let's set the scene. You created a table called my_faithful_test in Vertica with the following structure: [[See Video to Reveal this Text or Code Snippet]] Now, you want to remove the eruptions column with the following command: [[See Video to Reveal this Text or Code Snippet]] However, running this command leads to an error message: [[See Video to Reveal this Text or Code Snippet]] You want to drop the column, not the entire table! So how can you resolve this? Understanding the Root Cause The issue arises from how Vertica handles projections, particularly the first super projection created when the table is defined. When you create a table, Vertica often utilizes the first 8 columns for ORDER BY and SEGMENTED BY HASH() operations. This can lead to complications when trying to drop a column that plays a vital role in a projection. Key Takeaways: Super projections can restrict column modifications. Dropping a column that affects key projections often triggers errors. Solutions: Safely Dropping the Column If you're determined to keep your table intact while also dropping a problematic column, follow these steps: Step 1: Rename the Projection Start by renaming the existing projection that includes the offending column. This will effectively "park" it while you create a new setup. [[See Video to Reveal this Text or Code Snippet]] Step 2: Create a New Super Projection Next, create a new super projection without the column you want to drop. This projection should be structured to omit that column. [[See Video to Reveal this Text or Code Snippet]] Step 3: Refresh the Projection Subsequently, you need to refresh the new projection to ensure it holds the current data. [[See Video to Reveal this Text or Code Snippet]] Note: Make sure that your new projection has all the necessary nodes available before refreshing. Step 4: Clean Up Data Structures To keep your database clean and avoid confusion, execute the MAKE_AHM_NOW() function to remove any remaining delete vector ROS containers. [[See Video to Reveal this Text or Code Snippet]] Step 5: Drop the Old Projection Once your new projection is up and running, you can safely drop the renamed projection that includes the column you were aiming to delete. [[See Video to Reveal this Text or Code Snippet]] Step 6: Finally, Drop the Column Now that you've set up a new projection, you're free to drop the column safely: [[See Video to Reveal this Text or Code Snippet]] Conclusion Dropping a column in Vertica does not have to be a daunting task. By understanding the role of projections and following these structured steps, you can navigate through potential pitfalls effectively. This method allows you to retain your data integrity while making necessary adjustments to your table schemas. Next time you need to alter your Vertica tables, keep this guide handy to help streamline the process!