vbarua commented on code in PR #13511:
URL: https://github.com/apache/datafusion/pull/13511#discussion_r1979981659
##########
datafusion/expr/src/expr.rs:
##########
@@ -295,6 +295,8 @@ pub enum Expr {
/// See also [`ExprFunctionExt`] to set these fields.
///
/// [`ExprFunctionExt`]: crate::expr_fn::ExprFunctionExt
+ ///
+ /// cf. `WITHIN GROUP` is converted to `ORDER BY` internally in
`datafusion/sql/src/expr/function.rs`
Review Comment:
minor/opinionated: I'm not sure if it's worth mentioning this at all here.
`WITHIN GROUP` is effectively an `ORDER BY` specified differently. This only
matters at the SQL layer, and you handle and explain it there already.
##########
datafusion/sql/src/expr/function.rs:
##########
@@ -349,15 +365,49 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
} else {
// User defined aggregate functions (UDAF) have precedence in case
it has the same name as a scalar built-in function
if let Some(fm) = self.context_provider.get_aggregate_meta(&name) {
- let order_by = self.order_by_to_sort_expr(
- order_by,
- schema,
- planner_context,
- true,
- None,
- )?;
- let order_by = (!order_by.is_empty()).then_some(order_by);
- let args = self.function_args_to_expr(args, schema,
planner_context)?;
+ if fm.is_ordered_set_aggregate() && within_group.is_empty() {
+ return plan_err!("WITHIN GROUP clause is required when
calling ordered set aggregate function({})", fm.name());
+ }
+
+ if null_treatment.is_some() &&
!fm.supports_null_handling_clause() {
+ return plan_err!(
+ "[IGNORE | RESPECT] NULLS are not permitted for {}",
+ fm.name()
+ );
+ }
Review Comment:
Per my point about `[IGNORE | RESPECT] NULLS` being a property of _window
functions_, I don't think we need this check here.
##########
datafusion/sql/src/expr/function.rs:
##########
@@ -177,8 +180,14 @@ impl FunctionArgs {
}
}
- if !within_group.is_empty() {
- return not_impl_err!("WITHIN GROUP is not supported yet:
{within_group:?}");
+ if !within_group.is_empty() && order_by.is_some() {
+ return plan_err!("ORDER BY clause is only permitted in WITHIN
GROUP clause when a WITHIN GROUP is used");
+ }
+
+ if within_group.len() > 1 {
+ return not_impl_err!(
+ "Multiple column ordering in WITHIN GROUP clause is not
supported"
Review Comment:
Minor wording suggestion
```
Only a single ordering expression is permitted in a WITHIN GROUP clause
```
which explicitly points users to what they should do, instead of telling
them what they can't.
##########
datafusion/functions-aggregate/src/approx_percentile_cont.rs:
##########
@@ -51,29 +52,39 @@ create_func!(ApproxPercentileCont,
approx_percentile_cont_udaf);
/// Computes the approximate percentile continuous of a set of numbers
pub fn approx_percentile_cont(
- expression: Expr,
+ within_group: Sort,
Review Comment:
minor/opinionated: I think `order_by` would be a clearer name for this, as
the `WITHIN GROUP` is really just a wrapper around the `ORDER BY` clause.
##########
datafusion/sql/src/expr/function.rs:
##########
@@ -177,8 +180,14 @@ impl FunctionArgs {
}
}
- if !within_group.is_empty() {
- return not_impl_err!("WITHIN GROUP is not supported yet:
{within_group:?}");
+ if !within_group.is_empty() && order_by.is_some() {
+ return plan_err!("ORDER BY clause is only permitted in WITHIN
GROUP clause when a WITHIN GROUP is used");
Review Comment:
minor: I just noticed that in the block above there is a check for duplicate
order bys. I think it would be good to fold this into that check
```rust
FunctionArgumentClause::OrderBy(oby) => {
if order_by.is_some() { // can check for within group
here
return not_impl_err!("Calling {name}: Duplicated
ORDER BY clause in function arguments");
}
order_by = Some(oby);
}
```
to consolidate the handling into one place.
##########
datafusion/functions-aggregate/src/approx_percentile_cont.rs:
##########
@@ -131,6 +147,19 @@ impl ApproxPercentileCont {
args: AccumulatorArgs,
) -> Result<ApproxPercentileAccumulator> {
let percentile = validate_input_percentile_expr(&args.exprs[1])?;
+
+ let is_descending = args
+ .ordering_req
+ .first()
+ .map(|sort_expr| sort_expr.options.descending)
+ .unwrap_or(false);
+
+ let percentile = if is_descending {
+ 1.0 - percentile
+ } else {
+ percentile
+ };
Review Comment:
This seems reasonable to me, but I don't have that much experience on the
execution side of things.
##########
datafusion/expr/src/udaf.rs:
##########
@@ -845,6 +861,19 @@ pub trait AggregateUDFImpl: Debug + Send + Sync {
ScalarValue::try_from(data_type)
}
+ /// If this function supports `[IGNORE NULLS | RESPECT NULLS]` clause,
return true
+ /// If the function does not, return false
+ /// Otherwise return None (the default)
+ fn supports_null_handling_clause(&self) -> Option<bool> {
+ None
+ }
Review Comment:
This was smelling odd, so I dug a bit deeper. I think you've inadvertantly
stumbled into something even weirder than you anticipated
The example you've linked is
```sql
SELECT FIRST_VALUE(column1) RESPECT NULLS FROM t;
```
which I don't think is a valid query because `first_value` _should not_ be
an aggregate function, or at the very least the above query is not valid in
most SQL dialects. `first_value` is actually a window function in other engines
(eg. [Trino](https://trino.io/docs/current/functions/window.html#first_value),
[Postgres](https://www.postgresql.org/docs/17/functions-window.html),
[MySQL](https://dev.mysql.com/doc/refman/8.4/en/window-function-descriptions.html#function_first-value)).
If you try running something like
```sql
SELECT first_value(column1) FROM t;
```
against Postgres you get an error like
```
Query Error: window function first_value requires an OVER clause
```
[dbfiddle](https://www.db-fiddle.com/f/oMU1DDB2915nrHLKqUVj9a/0)
The `RESPECT NULLS | IGNORE NULLS` options is only a property of certain
_window_ functions, hence we shouldn't need to track it for aggregate functions.
I'm going to file a ticket for the above.
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