Github user scwf commented on a diff in the pull request:
https://github.com/apache/spark/pull/6104#discussion_r30567233
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/WindowFunctionDefinition.scala ---
@@ -0,0 +1,341 @@
+/*
+ * 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
+
+import scala.language.implicitConversions
+
+import org.apache.spark.annotation.Experimental
+import org.apache.spark.sql.catalyst.expressions._
+
+/**
+ * :: Experimental ::
+ * A set of methods for window function definition for aggregate
expressions.
+ * For example:
+ * {{{
+ * // predefine a window
+ * val w = partitionBy("name").orderBy("id")
+ *
+ * df.select(
+ * first("value")
+ * over(w).as("first_value"),
+ * last("value")
+ * over(w).as("last_value"),
+ * avg("value")
+ * over(
+ * partitionBy("k1")
+ * .orderBy("k2", "k3")
+ * .rows
+ * .following(1)).as("avg_value"),
+ * max("value")
+ * .over(
+ * partitionBy("k2")
+ * .orderBy("k3")
+ * .range
+ * .between
+ * .preceding(4)
+ * .and
+ * .following(3)).as("max_value"))
+ *
+ * }}}
+ *
+ * @param column The bounded the aggregate/window function
+ * @param partitionSpec The partition of the window
+ * @param orderSpec The ordering of the window
+ * @param frame The Window Frame type
+ * @param bindLower A hint of when call the methods `.preceding(n)`
`.currentRow()` `.following()`
+ * if bindLower == true, then we will set the lower
bound, otherwise, we should
+ * set the upper bound for the Row/Range Frame.
+ */
+@Experimental
+class WindowFunctionDefinition protected[sql](
--- End diff --
then i will suggest `WindowSpecDef`
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