Function plan_aggregate_common

src/sql/src/plan/query.rs:5206–5313

Common part of the planning of windowed and non-windowed aggregation functions.

(
    ecx: &ExprContext,
    Function::<Aug> {
        name,
        args,
        filter,
        over: _,
        distinct,
    }: &Function<Aug>,
)

/// Common part of the planning of windowed and non-windowed aggregation functions.
fn plan_aggregate_common(
    ecx: &ExprContext,
    Function::<Aug> {
        name,
        args,
        filter,
        over: _,
        distinct,
    }: &Function<Aug>,
) -> Result<AggregateExpr, PlanError> {
    // Normal aggregate functions, like `sum`, expect as input a single expression
    // which yields the datum to aggregate. Order sensitive aggregate functions,
    // like `jsonb_agg`, are special, and instead expect a Record whose first
    // element yields the datum to aggregate and whose successive elements yield
    // keys to order by. This expectation is hard coded within the implementation
    // of each of the order-sensitive aggregates. The specification of how many
    // order by keys to consider, and in what order, is passed via the `order_by`
    // field on the `AggregateFunc` variant.

    // While all aggregate functions support the ORDER BY syntax, it's a no-op for
    // most, so explicitly drop it if the function doesn't care about order. This
    // prevents the projection into Record below from triggering on unsupported
    // functions.

    let impls = match resolve_func(ecx, name, args)? {
        Func::Aggregate(impls) => impls,
        _ => bail_internal!("plan_aggregate_common called on non-aggregate function"),
    };

    // We follow PostgreSQL's rule here for mapping `count(*)` into the
    // generalized function selection framework. The rule is simple: the user
    // must type `count(*)`, but the function selection framework sees an empty
    // parameter list, as if the user had typed `count()`. But if the user types
    // `count()` directly, that is an error. Like PostgreSQL, we apply these
    // rules to all aggregates, not just `count`, since we may one day support
    // user-defined aggregates, including user-defined aggregates that take no
    // parameters.
    let (args, order_by) = match &args {
        FunctionArgs::Star => (vec![], vec![]),
        FunctionArgs::Args { args, order_by } => {
            if args.is_empty() {
                sql_bail!(
                    "{}(*) must be used to call a parameterless aggregate function",
                    humanize_or_debug(ecx.qcx.scx, name)
                );
            }
            let args = plan_exprs(ecx, args)?;
            (args, order_by.clone())
        }
    };

    let (order_by_exprs, col_orders) = plan_function_order_by(ecx, &order_by)?;

    let (mut expr, func) = func::select_impl(ecx, FuncSpec::Func(name), impls, args, col_orders)?;
    if let Some(filter) = &filter {
        // If a filter is present, as in
        //
        //     <agg>(<expr>) FILTER (WHERE <cond>)