konstantinb commented on PR #6505:
URL: https://github.com/apache/hive/pull/6505#issuecomment-4580556255
@zabetak there are two more considerations. One relates to "const null"
column statistics to which buildColStatForConstant() assigns an NDV of 0 while
the Hive metastore saves such columns with an NDV of 1:
`CREATE TABLE test_const_null_ndv (i INT, s STRING) STORED AS ORC;
INSERT INTO test_const_null_ndv VALUES (NULL, 'a'), (NULL, 'b');
DESCRIBE FORMATTED test_const_null_ndv i;
`
results in the describe output of
`POSTHOOK: Input: default@test_const_null_ndv
col_name i
data_type int
min
max
num_nulls 2
distinct_count 1
avg_col_len
max_col_len
num_trues
num_falses
bit_vector HL
comment from deserializer
COLUMN_STATS_ACCURATE
{\"BASIC_STATS\":\"true\",\"COLUMN_STATS\":{\"i\":\"true\",\"s\":\"true\"}}
`
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