java - Get TableSchema from BigQuery result PCollection<TableRow>

Question

When I run a query in BigQuery Web UI, the results are displayed in a table where both name and type of each field are known (even when a field is a result of COUNT(), AVG(), ... operation, type of field is known, of course). The results can be then directly exported as a table/json/csv.

My question is, when I retrieve query results in my java project, e.g. with a query:

String query =  "SELECT nationality, COUNT(DISTINCT personID) AS population 
                 FROM Dataset.Table 
                 GROUP BY nationality";

PCollection<TableRow> result = p.apply(BigQueryIO.Read.fromQuery(query));

... is it possible to obtain the schema of TableRow in result PCollection, without explicitly defining it? I think it must be possible, since it's possible with the same query when using BigQuery Web UI. But I can't figure out how to do it ...

TableSchema schema =  // function of PCollection<TableRow> result ?

result.apply(BigQueryIO.Write
                .named("Write Results Table")
                .to(getTableReference(tableName))
                .withSchema(schema));

That way query results could be always automatically exported/saved into a new table (only the table name then needs to be explicitly provided).

Any ideas? Any help would be appreciated :)

Answer 1

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