Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/15544#discussion_r139876729
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/ApproxCountDistinctForIntervals.scala
---
@@ -0,0 +1,235 @@
+/*
+ * 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.spark.sql.catalyst.expressions.aggregate
+
+import java.util
+
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.analysis.TypeCheckResult
+import
org.apache.spark.sql.catalyst.analysis.TypeCheckResult.{TypeCheckFailure,
TypeCheckSuccess}
+import org.apache.spark.sql.catalyst.expressions.{AttributeReference,
ExpectsInputTypes, Expression}
+import org.apache.spark.sql.catalyst.util.{ArrayData, GenericArrayData,
HyperLogLogPlusPlusHelper}
+import org.apache.spark.sql.types._
+
+/**
+ * This function counts the approximate number of distinct values (ndv) in
+ * intervals constructed from endpoints specified in
`endpointsExpression`. The endpoints should be
+ * sorted into ascending order. E.g., given an array of endpoints
+ * (endpoint_1, endpoint_2, ... endpoint_N), returns the approximate ndv's
for intervals
+ * [endpoint_1, endpoint_2], (endpoint_2, endpoint_3], ... (endpoint_N-1,
endpoint_N].
+ * To count ndv's in these intervals, apply the HyperLogLogPlusPlus
algorithm in each of them.
+ * @param child to estimate the ndv's of.
+ * @param endpointsExpression to construct the intervals, should be sorted
into ascending order.
--- End diff --
`An array expression with `NumericType` element to construct the intervals
.... Must be foldable.`
---
---------------------------------------------------------------------
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
