warehouse_queries is a query history: one row per query, with the table it read, how many of that table's partitions it scanned (partitions_scanned) out of how many exist (partitions_total), and the bytes it read.
A query that reads every partition of a table that has more than one partition pruned nothing — a full scan. Reading the only partition of a single-partition table isn't a pruning failure, and tables with a NULL partitions_total aren't partitioned at all; leave both out.
For each user with at least one full scan, return user_name, full_scans (how many) and full_scan_bytes (total bytes_scanned of those queries only). Sort by full_scan_bytes descending, then user_name.