Thank you for coming with this practical question. I have the answer for you.
“When your data is first loaded into the Transformer page, a sample of the data in your dataset is displayed in the data grid.”
“When a dataset is first created, a background job begins to generate a sample using the first set of rows of the dataset. This initial sample is usually very quick to generate, so that you can get to work right away on your transformations.”
The data you got in DataPrep table is only a small sample of source data when we ingest datasets from BigQuery to DataPrep. We need to submit it as jobs after you editing recipes. The output will consist the complete data set which could be saved as a new table in BigQuery directly.
Thank you for keeping learning.
Your AI servant,