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new 4b31aaa14c Fix constant value from stats (#20042)
4b31aaa14c is described below
commit 4b31aaa14c778df5856eafb71545000c6cfdd9f3
Author: Gabriel <[email protected]>
AuthorDate: Wed Jan 28 12:45:05 2026 +0100
Fix constant value from stats (#20042)
## Which issue does this PR close?
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enhancements and this helps us generate change logs for our releases.
You can link an issue to this PR using the GitHub syntax. For example
`Closes #123` indicates that this PR will close issue #123.
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- Closes https://github.com/apache/datafusion/issues/20041
## Rationale for this change
<!--
Why are you proposing this change? If this is already explained clearly
in the issue then this section is not needed.
Explaining clearly why changes are proposed helps reviewers understand
your changes and offer better suggestions for fixes.
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Fix a bug that appeared when reading constant values from stats
## What changes are included in this PR?
<!--
There is no need to duplicate the description in the issue here but it
is sometimes worth providing a summary of the individual changes in this
PR.
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- A 2-line bug fix
- A test that reproduces the issue on `main` and succeeds in this PR
## Are these changes tested?
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1. Prevent the code from being accidentally broken by subsequent changes
2. Serve as another way to document the expected behavior of the code
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Yes, by a new unit test.
Additionally, I tested this changes with
https://github.com/datafusion-contrib/datafusion-distributed and the
problem is solved also there.
## Are there any user-facing changes?
Nothing besides the bug fix
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---
.../core/src/datasource/physical_plan/parquet.rs | 48 ++++++++++++++++++++--
datafusion/datasource-parquet/src/opener.rs | 4 ++
2 files changed, 49 insertions(+), 3 deletions(-)
diff --git a/datafusion/core/src/datasource/physical_plan/parquet.rs
b/datafusion/core/src/datasource/physical_plan/parquet.rs
index 9b4733dbcc..4c6d915d5b 100644
--- a/datafusion/core/src/datasource/physical_plan/parquet.rs
+++ b/datafusion/core/src/datasource/physical_plan/parquet.rs
@@ -38,10 +38,10 @@ mod tests {
use crate::prelude::{ParquetReadOptions, SessionConfig, SessionContext};
use crate::test::object_store::local_unpartitioned_file;
use arrow::array::{
- ArrayRef, AsArray, Date64Array, Int8Array, Int32Array, Int64Array,
StringArray,
- StringViewArray, StructArray, TimestampNanosecondArray,
+ ArrayRef, AsArray, Date64Array, DictionaryArray, Int8Array, Int32Array,
+ Int64Array, StringArray, StringViewArray, StructArray,
TimestampNanosecondArray,
};
- use arrow::datatypes::{DataType, Field, Fields, Schema, SchemaBuilder};
+ use arrow::datatypes::{DataType, Field, Fields, Schema, SchemaBuilder,
UInt16Type};
use arrow::record_batch::RecordBatch;
use arrow::util::pretty::pretty_format_batches;
use arrow_schema::{SchemaRef, TimeUnit};
@@ -2263,6 +2263,48 @@ mod tests {
Ok(())
}
+ /// Tests that constant dictionary columns (where min == max in statistics)
+ /// are correctly handled. This reproduced a bug where the constant value
+ /// from statistics had type Utf8 but the schema expected Dictionary.
+ #[tokio::test]
+ async fn test_constant_dictionary_column_parquet() -> Result<()> {
+ let tmp_dir = TempDir::new()?;
+ let path = tmp_dir.path().to_str().unwrap().to_string() +
"/test.parquet";
+
+ // Write parquet with dictionary column where all values are the same
+ let schema = Arc::new(Schema::new(vec![Field::new(
+ "status",
+ DataType::Dictionary(Box::new(DataType::UInt16),
Box::new(DataType::Utf8)),
+ false,
+ )]));
+ let status: DictionaryArray<UInt16Type> =
+ vec!["active", "active"].into_iter().collect();
+ let batch = RecordBatch::try_new(schema.clone(),
vec![Arc::new(status)])?;
+ let file = File::create(&path)?;
+ let props = WriterProperties::builder()
+
.set_statistics_enabled(parquet::file::properties::EnabledStatistics::Page)
+ .build();
+ let mut writer = ArrowWriter::try_new(file, schema, Some(props))?;
+ writer.write(&batch)?;
+ writer.close()?;
+
+ // Query the constant dictionary column
+ let ctx = SessionContext::new();
+ ctx.register_parquet("t", &path, ParquetReadOptions::default())
+ .await?;
+ let result = ctx.sql("SELECT status FROM t").await?.collect().await?;
+
+ insta::assert_snapshot!(batches_to_string(&result),@r"
+ +--------+
+ | status |
+ +--------+
+ | active |
+ | active |
+ +--------+
+ ");
+ Ok(())
+ }
+
fn write_file(file: &String) {
let struct_fields = Fields::from(vec![
Field::new("id", DataType::Int64, false),
diff --git a/datafusion/datasource-parquet/src/opener.rs
b/datafusion/datasource-parquet/src/opener.rs
index c50905c224..6f92d567c8 100644
--- a/datafusion/datasource-parquet/src/opener.rs
+++ b/datafusion/datasource-parquet/src/opener.rs
@@ -739,6 +739,10 @@ fn constant_value_from_stats(
&& !min.is_null()
&& matches!(column_stats.null_count, Precision::Exact(0))
{
+ // Cast to the expected data type if needed (e.g., Utf8 -> Dictionary)
+ if min.data_type() != *data_type {
+ return min.cast_to(data_type).ok();
+ }
return Some(min.clone());
}
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