Method unparse_table_scan_pushdown

datafusion/sql/src/unparser/plan.rs:1663–1815

Try to unparse a table scan with pushdown operations into a new subquery plan. If the table scan is without any pushdown operations, return None.

(
        &self,
        plan: &LogicalPlan,
        alias: Option<TableReference>,
        already_projected: bool,
    )

    /// Try to unparse a table scan with pushdown operations into a new subquery plan.
    /// If the table scan is without any pushdown operations, return None.
    fn unparse_table_scan_pushdown(
        &self,
        plan: &LogicalPlan,
        alias: Option<TableReference>,
        already_projected: bool,
    ) -> Result<Option<LogicalPlan>> {
        match plan {
            LogicalPlan::TableScan(table_scan) => {
                if !Self::is_scan_with_pushdown(table_scan) {
                    return Ok(None);
                }
                let table_schema = table_scan.source.schema();
                let mut filter_alias_rewriter =
                    alias.as_ref().map(|alias_name| TableAliasRewriter {
                        table_schema: &table_schema,
                        alias_name: alias_name.clone(),
                    });

                let mut builder = LogicalPlanBuilder::scan(
                    table_scan.table_name.clone(),
                    Arc::clone(&table_scan.source),
                    None,
                )?;
                // We will rebase the column references to the new alias if it exists.
                // If the projection or filters are empty, we will append alias to the table scan.
                //
                // Example:
                //   select t1.c1 from t1 where t1.c1 > 1 -> select a.c1 from t1 as a where a.c1 > 1
                if let Some(ref alias) = alias
                    && (table_scan.projection.is_some() || !table_scan.filters.is_empty())
                {
                    builder = builder.alias(alias.clone())?;
                }

                // 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 && let Some(project_vec) = &table_scan.projection {
                    if project_vec.is_empty() {
                        builder = builder.project(self.empty_projection_fallback())?;
                    } else {
                        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)?;