Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/3743#discussion_r112482490
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/api/windows.scala
---
@@ -22,6 +22,126 @@ import org.apache.flink.table.expressions.{Expression,
ExpressionParser}
import org.apache.flink.table.plan.logical._
/**
+ * An over window specification.
+ *
+ * Over window is similar to the traditional OVER SQL.
+ */
+class OverWindow {
+
+ private[flink] var alias: Expression = _
+ private[flink] var partitionBy: Seq[Expression] = Seq[Expression]()
+ private[flink] var orderBy: Expression = _
+ private[flink] var preceding: Expression = _
+ private[flink] var following: Expression = null
+
+ /**
+ * Assigns an alias for this window that the following `select()`
clause can refer to.
+ *
+ * @param alias alias for this over window
+ * @return this over window
+ */
+ def as(alias: String): OverWindow =
as(ExpressionParser.parseExpression(alias))
+
+ /**
+ * Assigns an alias for this window that the following `select()`
clause can refer to.
+ *
+ * @param alias alias for this over window
+ * @return this over window
+ */
+ def as(alias: Expression): OverWindow = {
--- End diff --
I think it would be good if we could enforce the alias.
This could be done by first build a window which is not of type
`OverWindow` and letting `as()` return the complete `OverWindow`
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