Github user vvysotskyi commented on a diff in the pull request:
https://github.com/apache/drill/pull/805#discussion_r112650691
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/Metadata.java
---
@@ -1668,9 +1666,25 @@ public ColumnMetadata_v3(String[] name,
PrimitiveTypeName primitiveType, Object
return nulls;
}
+ /**
+ * Checks that the column chunk has single value.
+ * Returns true if minValue and maxValue are the same, but not null,
+ * and all column chunk values are not null.
+ * Returns true if minValue and maxValue are null and null values
count in
+ * the column chunk is greater than 0.
+ *
+ * @return true if column has single value
+ */
@Override
public boolean hasSingleValue() {
- return (minValue !=null && maxValue != null &&
minValue.equals(maxValue));
+ if (nulls != null) {
--- End diff --
Yes, we should apply it to ColumnMetadata_v1, thanks.
In ColumnMetadata_v2 mxValue is set only in the case when min value is the
same as the max value. So we could not be sure that if mxValue == null and
nulls count is greater than zero, column has single value.
Also I have changed the result for the second case described in your
previous comment. Statistics [1] for most parquet types use java primitive
types to store min and max values, so min/max can not be null even if the table
has null values. So I removed check nulls == 0.
[1]
https://github.com/apache/parquet-mr/tree/e54ca615f213f5db6d34d9163c97eec98920d7a7/parquet-column/src/main/java/org/apache/parquet/column/statistics
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