Method select_to_sql_expr

datafusion/sql/src/unparser/plan.rs:194–227

(
        &self,
        plan: &LogicalPlan,
        query: &mut Option<QueryBuilder>,
    )

    }

    fn select_to_sql_expr(
        &self,
        plan: &LogicalPlan,
        query: &mut Option<QueryBuilder>,
    ) -> Result<SetExpr> {
        let mut select_builder = SelectBuilder::default();
        select_builder.push_from(TableWithJoinsBuilder::default());
        let mut relation_builder = RelationBuilder::default();
        self.select_to_sql_recursively(
            plan,
            query,
            &mut select_builder,
            &mut relation_builder,
        )?;

        // If we were able to construct a full body (i.e. UNION ALL), return it
        if let Some(body) = query.as_mut().and_then(|q| q.take_body()) {
            return Ok(*body);
        }

        // If no projection is set, add a wildcard projection to the select
        // which will be translated to `SELECT *` in the SQL statement
        if !select_builder.already_projected() {
            select_builder.projection(vec![ast::SelectItem::Wildcard(
                ast::WildcardAdditionalOptions::default(),
            )]);
        }

        let mut twj = select_builder.pop_from().unwrap();
        twj.relation(relation_builder);
        select_builder.push_from(twj);

        Ok(SetExpr::Select(Box::new(select_builder.build()?)))
    }

    /// Reconstructs a SELECT SQL statement from a logical plan by unprojecting column expressions
    /// found in a [Projection] node. This requires scanning the plan tree for relevant Aggregate