René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`DataFrame.to_gbq` with `if_exists=\"replace\"` and `clustering_columns` can swap data between columns if order is different","articleBody":"#### Environment details\n\n```\nPython: 3.12.10 (main, Apr  9 2025, 03:49:38) [Clang 20.1.0 ]\nbigframes==2.37.0\ngoogle-cloud-bigquery==3.40.1\npandas==3.0.1\npyarrow==23.0.1\n```\n\n#### Steps to reproduce\n\n  1. Create a table with `Dataframe.to_gbq` with `clustering_columns`\n  2. Reorder the clustering column and another column that has the same type \n  3. Write the updated dataframe to the same table with `if_exists=\"replace\"`\n  4. Inspect the table to see columns with different data than in dataframe\n\n#### Code example\n\n```python\nimport bigframes.pandas as bpd\nimport pandas as pd\n\nTABLE_ID = \"my_project.my_dataset.test_table\"\n\ndf = pd.DataFrame(\n    {\"a\": [10, 1, 2], \"b\": [\"Justin\", \"Alex\", \"Jim\"], \"c\": [\"cat\", \"dog\", \"cat\"]}\n)\nbdf = bpd.DataFrame(df)\n\n# First time writing, all good\nbdf.to_gbq(TABLE_ID, clustering_columns=[\"b\"])\n\n# Reorder the clustered column b and column c\nbdf = bdf[[\"a\", \"c\", \"b\"]]\n\n# When replacing and writing, the b and c columns are swapped\nbdf.to_gbq(TABLE_ID, if_exists=\"replace\", clustering_columns=[\"b\"])\n```\n\nWhile the dataframe looks good, the updated table now has columns b/c data swapped:\n\n\u003cimg width=\"500\" alt=\"Image\" src=\"https://github.com/user-attachments/assets/ba5a77dc-d404-4590-bafc-b56ac165dc2b\" /\u003e\n\n\u003cimg width=\"500\" alt=\"Image\" src=\"https://github.com/user-attachments/assets/72119924-703c-490c-9a93-664f341a3c22\" /\u003e\n\nThis doesn't happen if `clustering_columns` is not used in my testing.","author":{"url":"https://github.com/jbandoro","@type":"Person","name":"jbandoro"},"datePublished":"2026-03-10T17:53:01.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/2502/python-bigquery-dataframes/issues/2502"}