haohuaijin commented on code in PR #8454:
URL: https://github.com/apache/arrow-datafusion/pull/8454#discussion_r1419900172
##########
datafusion/core/src/physical_optimizer/projection_pushdown.rs:
##########
@@ -245,12 +246,36 @@ fn try_swapping_with_streaming_table(
}
/// Unifies `projection` with its input (which is also a [`ProjectionExec`]).
-/// Two consecutive projections can always merge into a single projection.
fn try_unifying_projections(
projection: &ProjectionExec,
child: &ProjectionExec,
) -> Result<Option<Arc<dyn ExecutionPlan>>> {
let mut projected_exprs = vec![];
+ let mut column_ref_map: HashMap<Column, usize> = HashMap::new();
+
+ // Collect the column references usage in the outer projection.
+ projection.expr().iter().for_each(|(expr, _)| {
Review Comment:
We don't prevent `Column` and `Literal` push_down. We prevent other express
push_down, used to prevent multiple evaluation of an equal expression.
```rust
if column_ref_map.iter().any(|(column, count)| {
*count > 1 &&
!is_expr_trivial(&child.expr()[column.index()].0.clone())
}) {
return Ok(None);
}
```
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