[fix][runtime] Add first_val_agg function

Author: guojn1

parser/src/main/java/io/dingodb/expr/parser/DefaultFunFactory.java

@@ -36,6 +36,7 @@
 import io.dingodb.expr.runtime.op.VariadicOp;
 import io.dingodb.expr.runtime.op.aggregation.CountAgg;
 import io.dingodb.expr.runtime.op.aggregation.CountAllAgg;
+import io.dingodb.expr.runtime.op.aggregation.FirstValueAgg;
 import io.dingodb.expr.runtime.op.aggregation.MaxAgg;
 import io.dingodb.expr.runtime.op.aggregation.MinAgg;
 import io.dingodb.expr.runtime.op.aggregation.SingleValueAgg;
@@ -311,6 +312,7 @@ public DefaultFunFactory(@NonNull ExprConfig config) {
         registerUnaryFun(SumAgg.NAME, Exprs.SUM_AGG);
         registerUnaryFun(Sum0Agg.NAME, Exprs.SUM0_AGG);
         registerUnaryFun(SingleValueAgg.NAME, Exprs.SINGLE_VALUE_AGG);
+        registerUnaryFun(FirstValueAgg.NAME, Exprs.FIRST_VALUE_AGG);
     }
 
     @Override

runtime/src/main/java/io/dingodb/expr/runtime/expr/Exprs.java

@@ -43,6 +43,7 @@
 import io.dingodb.expr.runtime.op.VariadicOp;
 import io.dingodb.expr.runtime.op.aggregation.CountAgg;
 import io.dingodb.expr.runtime.op.aggregation.CountAllAgg;
+import io.dingodb.expr.runtime.op.aggregation.FirstValueAgg;
 import io.dingodb.expr.runtime.op.aggregation.MaxAgg;
 import io.dingodb.expr.runtime.op.aggregation.MinAgg;
 import io.dingodb.expr.runtime.op.aggregation.SingleValueAgg;
@@ -353,6 +354,7 @@ public final class Exprs {
     public static final SumAgg SUM_AGG = SumAgg.INSTANCE;
     public static final Sum0Agg SUM0_AGG = Sum0Agg.INSTANCE;
     public static final SingleValueAgg SINGLE_VALUE_AGG = SingleValueAgg.INSTANCE;
+    public static final FirstValueAgg FIRST_VALUE_AGG = FirstValueAgg.INSTANCE;
 
     private Exprs() {
     }

runtime/src/main/java/io/dingodb/expr/runtime/op/aggregation/FirstValueAgg.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2021 DataCanvas
+ *
+ * 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.
+ */
+
+package io.dingodb.expr.runtime.op.aggregation;
+
+import io.dingodb.expr.common.type.Type;
+import io.dingodb.expr.runtime.ExprConfig;
+import lombok.AccessLevel;
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+import java.io.Serial;
+
+@RequiredArgsConstructor(access = AccessLevel.PRIVATE)
+public class FirstValueAgg extends UnaryAgg {
+    public static final String NAME = "FIRST_VALUE_AGG";
+
+    public static final FirstValueAgg INSTANCE = new FirstValueAgg(null);
+
+    @Serial
+    private static final long serialVersionUID = -1444678046223537450L;
+
+    @Getter
+    private final Type type;
+
+    @Override
+    public Object first(@Nullable Object value, ExprConfig config) {
+        return value;
+    }
+
+    @Override
+    public Object add(@Nullable Object var, @Nullable Object value, ExprConfig config) {
+        return value;
+    }
+
+    @Override
+    public Object merge(@NonNull Object var1, @NonNull Object var2, ExprConfig config) {
+        return null;
+    }
+
+    @Override
+    public Object emptyValue() {
+        return null;
+    }
+}