Function apply_existential_subquery

src/sql/src/plan/lowering.rs:2021–2051

(
    id_gen: &mut mz_ore::id_gen::IdGen,
    outer: MirRelationExpr,
    col_map: &ColumnMap,
    cte_map: &mut CteMap,
    subquery_expr: HirRelationExpr,
    apply_requires_distinct_outer: bool,
  

}

fn apply_existential_subquery(
    id_gen: &mut mz_ore::id_gen::IdGen,
    outer: MirRelationExpr,
    col_map: &ColumnMap,
    cte_map: &mut CteMap,
    subquery_expr: HirRelationExpr,
    apply_requires_distinct_outer: bool,
    context: &Context,
) -> Result<MirRelationExpr, PlanError> {
    branch(
        id_gen,
        outer,
        col_map,
        cte_map,
        subquery_expr,
        apply_requires_distinct_outer,
        context,
        |id_gen, expr, get_inner, col_map, cte_map, context| {
            let exists = expr
                // compute for every row in get_inner
                .applied_to(id_gen, get_inner.clone(), col_map, cte_map, context)?
                // throw away actual values and just remember whether or not there were __any__ rows
                .distinct_by((0..get_inner.arity()).collect())
                // Append true to anything that returned any rows.
                .map(vec![MirScalarExpr::literal_true()]);

            // append False to anything that didn't return any rows
            get_inner.lookup(id_gen, exists, vec![(Datum::False, ReprScalarType::Bool)])
        },
    )
}

impl AggregateExpr {
    fn applied_to(