Data engineering·Files, formats and table layers
you filtered on the partition column and the engine opened four folders instead of nine hundred.
Partition pruning
Also calledpartition elimination
Skipping whole partitions because the query's filter proves they cannot contain matching rows. It is the coarsest and by far the most valuable form of skipping, which is why partition column choice is the most consequential physical decision in a warehouse. It fails silently when the filter is on a derived expression the engine cannot see through, so a function wrapped around the partition column can turn a two-second query into a full scan.