sgrebnov commented on code in PR #13267:
URL: https://github.com/apache/datafusion/pull/13267#discussion_r1830100022
##########
datafusion/sql/src/unparser/plan.rs:
##########
@@ -725,24 +727,29 @@ impl Unparser<'_> {
}
}
- if let Some(project_vec) = &table_scan.projection {
- let project_columns = project_vec
- .iter()
- .cloned()
- .map(|i| {
- let schema = table_scan.source.schema();
- let field = schema.field(i);
- if alias.is_some() {
- Column::new(alias.clone(),
field.name().clone())
- } else {
- Column::new(
- Some(table_scan.table_name.clone()),
- field.name().clone(),
- )
- }
- })
- .collect::<Vec<_>>();
- builder = builder.project(project_columns)?;
+ // Avoid creating a duplicate Projection node, which would
result in an additional subquery if a projection already exists.
+ // For example, if the `optimize_projection` rule is applied,
there will be a Projection node, and duplicate projection
+ // information included in the TableScan node.
+ if !already_projected {
Review Comment:
This prevents from generating queries like `SELECT a, b from (SELECT a, b
from my_table)`.
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