Data engineering·Files, formats and table layers
the where-clause is handed to the file reader, which uses the min and max in each chunk's footer to skip most of them unread.
Predicate pushdown
Also calledfilter pushdown, row group skipping
Pushing a query's filters down to the storage layer so entire blocks can be excluded before decoding. Its effectiveness depends entirely on physical layout: min/max statistics only help if the filtered column is correlated with the file's ordering, which is why sorting on the column you filter by is worth more than most query tuning. When someone says a filter 'did nothing for cost', this is the mechanism that failed.