To transfer a CLOB (Character Large Object) from Oracle to BigQuery, follow these steps:
1. Extract CLOB Data from Oracle
You need to extract the CLOB data in manageable chunks, as shown in the error message, because the CLOB data size exceeds the buffer limit. Use one of the following methods:
Option A: Using DBMS_LOB.SUBSTR
SELECT DBMS_LOB.SUBSTR(wo_task_card_xml, 4000, 1) AS clob_chunk
FROM odb.wo_task_card
WHERE wo_task_card_xml IS NOT NULL;
This extracts the first 4000 characters of the CLOB. Repeat the process for the remaining chunks by adjusting the starting position.
Option B: Export the Entire CLOB
Use Oracle SQL Developer or a similar tool to export the full CLOB content into a text or CSV file.
2. Save the Extracted Data
• Save the CLOB data into a file in a readable format (e.g., .csv, .json).
• Ensure the file adheres to BigQuery’s schema requirements.
3. Prepare BigQuery Schema
BigQuery does not support CLOBs directly. Instead, store the CLOB as a STRING or JSON in BigQuery. Define a column with a STRING type in your BigQuery table.
4. Load Data into BigQuery
Use one of these methods to load data:
Option A: BigQuery Console
1. Upload the exported file via the BigQuery web interface.
2. Map the CLOB field to the STRING column.
Option B: BigQuery CLI
Use the bq command-line tool:
bq load --source_format=CSV your_dataset.your_table path_to_file.csv schema.json
Option C: Dataflow/ETL Tools
Use tools like Google Dataflow, Apache Beam, or Fivetran for automated CLOB extraction and transfer.
Additional Notes
• Ensure that your CLOB data is UTF-8 encoded to avoid character encoding issues.
• If the CLOB contains XML/JSON, validate it before loading into BigQuery.
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