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 driver offloads as much of the SELECT statement processing as possible to Open Exchange Rates and then processes the rest of the query in memory. In this way, the driver can execute unsupported predicates, joins, and aggregation.
When SupportEnhancedSQL = false, the driver limits SQL execution to what is supported by the Open Exchange Rates API.
Execution of Predicates
The driver 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 driver to filter effectively for even very large datasets.
Execution of Joins
The driver uses various techniques to join in memory. The driver trades off memory utilization against the requirement of reading the same table more than once.
Execution of Aggregates
The driver retrieves all rows necessary to process the aggregation in memory.