ENH: Read BigQuery query table without a query

[tswast]

It can cost a lot to run a SELECT * FROM my_table query, and yet from an API perspective, this query is completely unnecessary, as one can list the rows from the table directly for free with tabledata.list. I propose

df = pandas_gbq.read_gbq("my-project.my_dataset.my_table")

which will download a table directly (using bigquery_client.list_rows().to_dataframe()). Since all queries must contain some kind of whitespace and table IDs cannot contain any whitespace, we can use that to disambiguate query versus table ID.

[max-sixty]

I didn't know about that - I had thought you could run a preview, but not download a whole table that way.

Not opposed to it. I'm not sure it's that helpful given than a large enough table to be expensive to query is also impractical to download over JSON into memory.
But that's not an argument to not have the functionality, am +0 !

[tswast]

I think this feature would help with testing #365, as I realized I'm using the google-cloud-bigquery bigquery_client.list_rows(table_id).to_dataframe(...) pattern in #442 which doesn't actually test the full round trip via pandas-gbq.