Description:

Big query polymorphic table function (PTF) query fails when the output projection of native query involves any non-lower case column names.
Query SELECT * FROM TABLE(bigquery.system.query(query => 'select 1 as lower, 2 as UPPER, 3 as miXED'))

The above query throws an Internal server exception due to a mismatch in the following line since the Trino internal column name doesn't match the projected column name.
https://github.com/trinodb/trino/blob/406/plugin/trino-bigquery/src/main/java/io/trino/plugin/bigquery/BigQueryMetadata.java#L710

Another workaround without the fix is always to alias the column names to be lowercase.