[GitHub] [flink] swuferhong commented on a diff in pull request #20243: [FLINK-28491][table-planner] Introduce APPROX_COUNT_DISTINCT aggregate function for batch sql

[GitBox <gi...@apache.org>]

swuferhong commented on code in PR #20243:
URL: https://github.com/apache/flink/pull/20243#discussion_r922784619


##########
flink-table/flink-table-runtime/src/main/java/org/apache/flink/table/runtime/functions/aggregate/BatchApproxCountDistinctAggFunctions.java:
##########
@@ -0,0 +1,333 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.flink.table.runtime.functions.aggregate;
+
+import org.apache.flink.core.memory.MemorySegment;
+import org.apache.flink.core.memory.MemorySegmentFactory;
+import org.apache.flink.table.api.DataTypes;
+import org.apache.flink.table.data.DecimalData;
+import org.apache.flink.table.data.TimestampData;
+import org.apache.flink.table.data.binary.BinaryStringData;
+import org.apache.flink.table.runtime.functions.aggregate.hyperloglog.HllBuffer;
+import org.apache.flink.table.runtime.functions.aggregate.hyperloglog.HyperLogLogPlusPlus;
+import org.apache.flink.table.types.DataType;
+import org.apache.flink.table.types.logical.BigIntType;
+import org.apache.flink.table.types.logical.DateType;
+import org.apache.flink.table.types.logical.DecimalType;
+import org.apache.flink.table.types.logical.DoubleType;
+import org.apache.flink.table.types.logical.FloatType;
+import org.apache.flink.table.types.logical.IntType;
+import org.apache.flink.table.types.logical.LocalZonedTimestampType;
+import org.apache.flink.table.types.logical.LogicalType;
+import org.apache.flink.table.types.logical.SmallIntType;
+import org.apache.flink.table.types.logical.TimeType;
+import org.apache.flink.table.types.logical.TimestampType;
+import org.apache.flink.table.types.logical.TinyIntType;
+import org.apache.flink.table.types.logical.VarCharType;
+
+import java.util.Collections;
+import java.util.List;
+
+import static org.apache.flink.table.runtime.functions.aggregate.hyperloglog.XXH64.DEFAULT_SEED;
+import static org.apache.flink.table.runtime.functions.aggregate.hyperloglog.XXH64.hashInt;
+import static org.apache.flink.table.runtime.functions.aggregate.hyperloglog.XXH64.hashLong;
+import static org.apache.flink.table.runtime.functions.aggregate.hyperloglog.XXH64.hashUnsafeBytes;
+import static org.apache.flink.table.types.utils.DataTypeUtils.toInternalDataType;
+
+/** Built-in APPROX_COUNT_DISTINCT aggregate function for Batch sql. */
+public class BatchApproxCountDistinctAggFunctions {
+
+    /** Base function for APPROX_COUNT_DISTINCT aggregate. */
+    public abstract static class ApproxCountDistinctAggFunction<T>
+            extends BuiltInAggregateFunction<Long, HllBuffer> {
+
+        private static final Double RELATIVE_SD = 0.01;

Review Comment:
   I think here need to add some comments to explain why choose 0.01 ?



##########
flink-table/flink-table-planner/src/test/scala/org/apache/flink/table/planner/runtime/batch/sql/agg/SortAggITCase.scala:
##########
@@ -310,6 +312,57 @@ class SortAggITCase extends AggregateITCaseBase("SortAggregate") {
       Seq(row("null"))
     )
   }
+
+  @Test
+  def testApproximateCountDistinct(): Unit = {
+    val dataId = TestValuesTableFactory.registerData(TestData.fullDataTypesData)
+    tEnv.executeSql(
+      s"""
+         |CREATE TABLE MyTable (
+         |  `boolean` BOOLEAN,
+         |  `byte` TINYINT,
+         |  `short` SMALLINT,
+         |  `int` INT,
+         |  `long` BIGINT,
+         |  `float` FLOAT,
+         |  `double` DOUBLE,
+         |  `decimal52` DECIMAL(5, 2),

Review Comment:
   Adding more decimal types, like decimal (14, 2) and decimal (38, 2).



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