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There is some smart logic behind querying partitioned tables. If you filter on the partition column only, the data is actually not loaded into memory until you actually do some operations on it. So the first query doesn’t have to load all the data, just references to that specific partition. Then the second query does need to read in the data because you are querying an actual column in the table, so now q has to read the filtering column to find which rows match, and since you didn’t specify which columns to keep, it must also load the rest of the columns and filter them.