fix(agg): fix first_value and last_value to not ignore NULLs

src/expr/impl/src/aggregate/first_last_value.rs

@@ -0,0 +1,88 @@
+// Copyright 2024 RisingWave Labs
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use risingwave_common::types::{Datum, ScalarRefImpl};
+use risingwave_common_estimate_size::EstimateSize;
+use risingwave_expr::aggregate;
+use risingwave_expr::aggregate::AggStateDyn;
+
+/// Note that different from `min` and `max`, `first_value` doesn't ignore `NULL` values.
+///
+/// ```slt
+/// statement ok
+/// create table t(v1 int, ts int);
+///
+/// statement ok
+/// insert into t values (null, 1), (2, 2), (null, 3);
+///
+/// query I
+/// select first_value(v1 order by ts) from t;
+/// ----
+/// NULL
+///
+/// statement ok
+/// drop table t;
+/// ```
+#[aggregate("first_value(any) -> any")]
+fn first_value(state: &mut FirstValueState, input: Option<ScalarRefImpl<'_>>) {
+    if state.0.is_none() {
+        state.0 = Some(input.map(|x| x.into_scalar_impl()));
+    }
+}
+
+#[derive(Debug, Clone, Default, EstimateSize)]
+struct FirstValueState(Option<Datum>);
+
+impl AggStateDyn for FirstValueState {}
+
+impl From<&FirstValueState> for Datum {
+    fn from(state: &FirstValueState) -> Self {
+        if let Some(state) = &state.0 {
+            state.clone()
+        } else {
+            None
+        }
+    }
+}
+
+/// Note that different from `min` and `max`, `last_value` doesn't ignore `NULL` values.
+///
+/// ```slt
+/// statement ok
+/// create table t(v1 int, ts int);
+///
+/// statement ok
+/// insert into t values (null, 1), (2, 2), (null, 3);
+///
+/// query I
+/// select last_value(v1 order by ts) from t;
+/// ----
+/// NULL
+///
+/// statement ok
+/// drop table t;
+/// ```
+#[aggregate("last_value(*) -> auto", state = "ref")] // TODO(rc): `last_value(any) -> any`
+fn last_value<T>(_: Option<T>, input: Option<T>) -> Option<T> {
+    input
+}
+
+#[aggregate("internal_last_seen_value(*) -> auto", state = "ref", internal)]
+fn internal_last_seen_value<T>(state: T, input: T, retract: bool) -> T {
+    if retract {
+        state
+    } else {
+        input
+    }
+}

src/expr/impl/src/aggregate/general.rs

@@ -124,25 +124,6 @@ fn max<T: Ord>(state: T, input: T) -> T {
     state.max(input)
 }
 
-#[aggregate("first_value(*) -> auto", state = "ref")]
-fn first_value<T>(state: T, _: T) -> T {
-    state
-}
-
-#[aggregate("last_value(*) -> auto", state = "ref")]
-fn last_value<T>(_: T, input: T) -> T {
-    input
-}
-
-#[aggregate("internal_last_seen_value(*) -> auto", state = "ref", internal)]
-fn internal_last_seen_value<T>(state: T, input: T, retract: bool) -> T {
-    if retract {
-        state
-    } else {
-        input
-    }
-}
-
 /// Note the following corner cases:
 ///
 /// ```slt

src/expr/impl/src/aggregate/mod.rs

@@ -20,6 +20,7 @@ mod bit_or;
 mod bit_xor;
 mod bool_and;
 mod bool_or;
+mod first_last_value;
 mod general;
 mod jsonb_agg;
 mod mode;

src/tests/sqlsmith/src/sql_gen/scalar.rs

@@ -81,11 +81,15 @@ impl<R: Rng> SqlGenerator<'_, R> {
                 data_type: AstDataType::SmallInt,
                 value: self.gen_int(i16::MIN as isize, i16::MAX as isize),
             })),
-            T::Varchar => Expr::Value(Value::SingleQuotedString(
-                (0..10)
-                    .map(|_| self.rng.sample(Alphanumeric) as char)
-                    .collect(),
-            )),
+            T::Varchar => Expr::Cast {
+                // since we are generating random scalar literal, we should cast it to avoid unknown type
+                expr: Box::new(Expr::Value(Value::SingleQuotedString(
+                    (0..10)
+                        .map(|_| self.rng.sample(Alphanumeric) as char)
+                        .collect(),
+                ))),
+                data_type: AstDataType::Varchar,
+            },
             T::Decimal => Expr::Nested(Box::new(Expr::Value(Value::Number(self.gen_float())))),
             T::Float64 => Expr::Nested(Box::new(Expr::TypedString {
                 data_type: AstDataType::Float(None),