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The goal of the column statistics is that for each column, the writer
records the count and depending on the type other useful fields. For
most of the primitive types, it records the minimum and maximum
values; and for numeric types it additionally stores the sum.
From Hive 1.21.0 onwards, the column statistics will also record if
there are any null value within the row group by setting hasNull flag.
hasNull flag is used by ORC's predicate pushdown to better answer
'IS NULL' queries.

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