Function plan_using_constraint

src/sql/src/plan/query.rs:3858–4045

(
    column_names: &[ColumnName],
    left_qcx: &QueryContext,
    left: HirRelationExpr,
    left_scope: Scope,
    right_qcx: &QueryContext,
    right: HirRelationExpr,
    right_scope: Scope,
    

// See page 440 of ANSI SQL 2016 spec for details on scoping of using/natural joins
#[allow(clippy::too_many_arguments)]
fn plan_using_constraint(
    column_names: &[ColumnName],
    left_qcx: &QueryContext,
    left: HirRelationExpr,
    left_scope: Scope,
    right_qcx: &QueryContext,
    right: HirRelationExpr,
    right_scope: Scope,
    kind: JoinKind,
    alias: Option<&Ident>,
) -> Result<(HirRelationExpr, Scope), PlanError> {
    let mut both_scope = left_scope.clone().product(right_scope.clone())?;

    // Cargo culting PG here; no discernable reason this must fail, but PG does
    // so we do, as well.
    let mut unique_column_names = BTreeSet::new();
    for c in column_names {
        if !unique_column_names.insert(c) {
            return Err(PlanError::Unsupported {
                feature: format!(
                    "column name {} appears more than once in USING clause",
                    c.quoted()
                ),
                discussion_no: None,
            });
        }
    }

    let alias_item_name = alias.map(|alias| PartialItemName {
        database: None,
        schema: None,
        item: alias.clone().to_string(),
    });

    if let Some(alias_item_name) = &alias_item_name {
        for partial_item_name in both_scope.table_names() {
            if partial_item_name.matches(alias_item_name) {
                sql_bail!(
                    "table name \"{}\" specified more than once",
                    alias_item_name
                )
            }
        }
    }

    let ecx = &ExprContext {
        qcx: right_qcx,
        name: "USING clause",
        scope: &both_scope,
        relation_type: &SqlRelationType::new(
            left_qcx
                .relation_type(&left)
                .column_types
                .into_iter()
                .chain(right_qcx.relation_type(&right).column_types)
                .collect(),
        ),
        allow_aggregates: false,