Function unproject_unnest_expr

datafusion/sql/src/unparser/utils.rs:168–189

Recursively identify Column expressions and transform them into the appropriate unnest expression For example, if expr contains the column expr "__unnest_placeholder(make_array(Int64(1),Int64(2),Int64(2),Int64(5),NULL),depth=1)" it will be transformed into an actual unnest expression UNNEST([1, 2, 2, 5, NULL])

(expr: Expr, unnest: &Unnest)

/// For example, if expr contains the column expr "__unnest_placeholder(make_array(Int64(1),Int64(2),Int64(2),Int64(5),NULL),depth=1)"
/// it will be transformed into an actual unnest expression UNNEST([1, 2, 2, 5, NULL])
pub(crate) fn unproject_unnest_expr(expr: Expr, unnest: &Unnest) -> Result<Expr> {
    expr.transform(|sub_expr| {
            if let Expr::Column(col_ref) = &sub_expr {
                // Check if the column is among the columns to run unnest on. 
                // Currently, only List/Array columns (defined in `list_type_columns`) are supported for unnesting. 
                if unnest.list_type_columns.iter().any(|e| e.1.output_column.name == col_ref.name) {
                    if let Ok(idx) = unnest.schema.index_of_column(col_ref)
                        && let LogicalPlan::Projection(Projection { expr, .. }) = unnest.input.as_ref()
                            && let Some(unprojected_expr) = expr.get(idx) {
                                let unnest_expr = Expr::Unnest(expr::Unnest::new(unprojected_expr.clone()));
                                return Ok(Transformed::yes(unnest_expr));
                            }
                    return internal_err!(
                        "Tried to unproject unnest expr for column '{}' that was not found in the provided Unnest!", &col_ref.name
                    );
                }
            }

            Ok(Transformed::no(sub_expr))

        }).map(|e| e.data)
}

/// Like `unproject_unnest_expr`, but for Snowflake FLATTEN:
/// transforms `__unnest_placeholder(...)` column references into