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It seems that you’re encountering a common issue within BigQuery and JSONL format. First, JSON by nature does not maintain the order of its keys (or in this case, columns). This is a property of the data structure itself, since JSON objects are unordered sets of key-value pairs. Hence, the issue you are experiencing with the column order being different after export and import.
Secondly, concerning missing NULLs in your JSON file. NULLs are typically not included in JSON data due to normalization, to save on space and increase efficiency. This is actually a common practice in JSON serialization and not limited to Google BigQuery or GA4. Consequently, when you export data to JSONL and there are NULL values, those keys are usually not included in the serialized JSON object.
To work around this, you need to address these nuances during the import/export process. For example, if you require NULLs to be present in the JSON document, you may need to perform a preprocessing step to fill NULLs with a default value before exporting. To address the issue with column order, you will have to enforce that explicitly during the import process, as the order is not preserved naturally in JSON/JSONL format.
However, you’ll need to be aware that these adjustments could potentially alter the data structure and possibly affect your data analysis and further processing of these data.
