fix: ensure df in empty parquet (#16621)

pola-rs · May 31, 2024 · 6e88f1d · 6e88f1d
1 parent 7c7e834
commit 6e88f1d
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Showing 2 changed files with 14 additions and 1 deletion.
diff --git a/crates/polars-io/src/parquet/read/read_impl.rs b/crates/polars-io/src/parquet/read/read_impl.rs
@@ -779,10 +779,13 @@ impl BatchedParquetReader {
                     self.chunks_fifo.push_back(df)
                 }
             }
+        } else {
+            skipped_all_rgs = !self.has_returned;
         };
 
         if self.chunks_fifo.is_empty() {
             if skipped_all_rgs {
+                self.has_returned = true;
                 Ok(Some(vec![materialize_empty_df(
                     Some(self.projection.as_ref()),
                     &self.schema,
@@ -803,7 +806,7 @@ impl BatchedParquetReader {
                 }
             }
 
-            self.has_returned |= true;
+            self.has_returned = true;
             Ok(Some(chunks))
         }
     }

diff --git a/py-polars/tests/unit/streaming/test_streaming_io.py b/py-polars/tests/unit/streaming/test_streaming_io.py
@@ -268,3 +268,13 @@ def test_parquet_eq_statistics(monkeypatch: Any, capfd: Any, tmp_path: Path) ->
             "parquet file can be skipped, the statistics were sufficient"
             " to apply the predicate." in captured
         )
+
+
+@pytest.mark.write_disk()
+def test_streaming_empty_parquet_16523(tmp_path: Path) -> None:
+    file_path = tmp_path / "foo.parquet"
+    df = pl.DataFrame({"a": []}, schema={"a": pl.Int32})
+    df.write_parquet(file_path)
+    q = pl.scan_parquet(file_path)
+    q2 = pl.LazyFrame({"a": [1]}, schema={"a": pl.Int32})
+    assert q.join(q2, on="a").collect(streaming=True).shape == (0, 1)