This property enhances SQL functionality beyond what can be supported through the API directly, by enabling in-memory client-side processing.
When SupportEnhancedSQL = true, the component offloads as much of the SELECT statement processing as possible to Google Data Catalog and then processes the rest of the query in memory. In this way, the component can execute unsupported predicates, joins, and aggregation.
When SupportEnhancedSQL = false, the component limits SQL execution to what is supported by the Google Data Catalog API.
Execution of Predicates
The component determines which of the clauses are supported by the data source and then pushes them to the source to get the smallest superset of rows that would satisfy the query. It then filters the rest of the rows locally. The filter operation is streamed, which enables the component to filter effectively for even very large datasets.
Execution of Joins
The component uses various techniques to join in memory. The component trades off memory utilization against the requirement of reading the same table more than once.
Execution of Aggregates
The component retrieves all rows necessary to process the aggregation in memory.