Method empty_projection_fallback

datafusion/sql/src/unparser/plan.rs:2019–2025

Generates appropriate projection expression for empty projection lists. Returns an empty vec for dialects supporting empty select lists, or a dummy literal `1` for other dialects.

(&self)

    /// Returns an empty vec for dialects supporting empty select lists,
    /// or a dummy literal `1` for other dialects.
    fn empty_projection_fallback(&self) -> Vec<Expr> {
        if self.dialect.supports_empty_select_list() {
            Vec::new()
        } else {
            vec![Expr::Literal(ScalarValue::Int64(Some(1)), None)]
        }
    }

    /// Decides where extracted table-scan filters belong in the unparsed SQL:
    /// in the `JOIN ON` clause or in `WHERE`.