序
本文主要研究一下flink Table的Over Windows
实例
Table table = input
.window([OverWindow w].as("w")) // define over window with alias w
.select("a, b.sum over w, c.min over w"); // aggregate over the over window w
- Over Windows类似SQL的over子句，它可以基于event-time、processing-time或者row-count；具体可以通过Over类来构造，其中必须设置orderBy、preceding及as方法；它有Unbounded及Bounded两大类
Unbounded Over Windows实例
// Unbounded Event-time over window (assuming an event-time attribute "rowtime")
.window(Over.partitionBy("a").orderBy("rowtime").preceding("unbounded_range").as("w"));
// Unbounded Processing-time over window (assuming a processing-time attribute "proctime")
.window(Over.partitionBy("a").orderBy("proctime").preceding("unbounded_range").as("w"));
// Unbounded Event-time Row-count over window (assuming an event-time attribute "rowtime")
.window(Over.partitionBy("a").orderBy("rowtime").preceding("unbounded_row").as("w"));
// Unbounded Processing-time Row-count over window (assuming a processing-time attribute "proctime")
.window(Over.partitionBy("a").orderBy("proctime").preceding("unbounded_row").as("w"));
- 对于event-time及processing-time使用unbounded_range来表示Unbounded，对于row-count使用unbounded_row来表示Unbounded
Bounded Over Windows实例
// Bounded Event-time over window (assuming an event-time attribute "rowtime")
.window(Over.partitionBy("a").orderBy("rowtime").preceding("1.minutes").as("w"))
// Bounded Processing-time over window (assuming a processing-time attribute "proctime")
.window(Over.partitionBy("a").orderBy("proctime").preceding("1.minutes").as("w"))
// Bounded Event-time Row-count over window (assuming an event-time attribute "rowtime")
.window(Over.partitionBy("a").orderBy("rowtime").preceding("10.rows").as("w"))
// Bounded Processing-time Row-count over window (assuming a processing-time attribute "proctime")
.window(Over.partitionBy("a").orderBy("proctime").preceding("10.rows").as("w"))
- 对于event-time及processing-time使用诸如1.minutes来表示Bounded，对于row-count使用诸如10.rows来表示Bounded
Table.window
flink-table_2.11-1.7.0-sources.jar!/org/apache/flink/table/api/table.scala
class Table(
private[flink] val tableEnv: TableEnvironment,
private[flink] val logicalPlan: LogicalNode) {
//......
@varargs
def window(overWindows: OverWindow*): OverWindowedTable = {
if (tableEnv.isInstanceOf[BatchTableEnvironment]) {
throw new TableException("Over-windows for batch tables are currently not supported.")
}
if (overWindows.size != 1) {
throw new TableException("Over-Windows are currently only supported single window.")
}
new OverWindowedTable(this, overWindows.toArray)
}
//......
}
- Table提供了OverWindow参数的window方法，用来进行Over Windows操作，它创建的是OverWindowedTable
OverWindow
flink-table_2.11-1.7.0-sources.jar!/org/apache/flink/table/api/windows.scala
/**
* Over window is similar to the traditional OVER SQL.
*/
case class OverWindow(
private[flink] val alias: Expression,
private[flink] val partitionBy: Seq[Expression],
private[flink] val orderBy: Expression,
private[flink] val preceding: Expression,
private[flink] val following: Expression)
- OverWindow定义了alias、partitionBy、orderBy、preceding、following属性
Over
flink-table_2.11-1.7.0-sources.jar!/org/apache/flink/table/api/java/windows.scala
object Over {
/**
* Specifies the time attribute on which rows are grouped.
*
* For streaming tables call [[orderBy 'rowtime or orderBy 'proctime]] to specify time mode.
*
* For batch tables, refer to a timestamp or long attribute.
*/
def orderBy(orderBy: String): OverWindowWithOrderBy = {
val orderByExpr = ExpressionParser.parseExpression(orderBy)
new OverWindowWithOrderBy(Array[Expression](), orderByExpr)
}
/**
* Partitions the elements on some partition keys.
*
* @param partitionBy some partition keys.
* @return A partitionedOver instance that only contains the orderBy method.
*/
def partitionBy(partitionBy: String): PartitionedOver = {
val partitionByExpr = ExpressionParser.parseExpressionList(partitionBy).toArray
new PartitionedOver(partitionByExpr)
}
}
class OverWindowWithOrderBy(
private val partitionByExpr: Array[Expression],
private val orderByExpr: Expression) {
/**
* Set the preceding offset (based on time or row-count intervals) for over window.
*
* @param preceding preceding offset relative to the current row.
* @return this over window
*/
def preceding(preceding: String): OverWindowWithPreceding = {
val precedingExpr = ExpressionParser.parseExpression(preceding)
new OverWindowWithPreceding(partitionByExpr, orderByExpr, precedingExpr)
}
}
class PartitionedOver(private val partitionByExpr: Array[Expression]) {
/**
* Specifies the time attribute on which rows are grouped.
*
* For streaming tables call [[orderBy 'rowtime or orderBy 'proctime]] to specify time mode.
*
* For batch tables, refer to a timestamp or long attribute.
*/
def orderBy(orderBy: String): OverWindowWithOrderBy = {
val orderByExpr = ExpressionParser.parseExpression(orderBy)
new OverWindowWithOrderBy(partitionByExpr, orderByExpr)
}
}
class OverWindowWithPreceding(
private val partitionBy: Seq[Expression],
private val orderBy: Expression,
private val preceding: Expression) {
private[flink] var following: Expression = _
/**
* Assigns an alias for this window that the following `select()` clause can refer to.
*
* @param alias alias for this over window
* @return 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 over window
*/
def as(alias: Expression): OverWindow = {
// set following to CURRENT_ROW / CURRENT_RANGE if not defined
if (null == following) {
if (preceding.resultType.isInstanceOf[RowIntervalTypeInfo]) {
following = CURRENT_ROW
} else {
following = CURRENT_RANGE
}
}
OverWindow(alias, partitionBy, orderBy, preceding, following)
}
/**
* Set the following offset (based on time or row-count intervals) for over window.
*
* @param following following offset that relative to the current row.
* @return this over window
*/
def following(following: String): OverWindowWithPreceding = {
this.following(ExpressionParser.parseExpression(following))
}
/**
* Set the following offset (based on time or row-count intervals) for over window.
*
* @param following following offset that relative to the current row.
* @return this over window
*/
def following(following: Expression): OverWindowWithPreceding = {
this.following = following
this
}
}
- Over类是创建over window的帮助类，它提供了orderBy及partitionBy两个方法，分别创建的是OverWindowWithOrderBy及PartitionedOver
- PartitionedOver提供了orderBy方法，创建的是OverWindowWithOrderBy；OverWindowWithOrderBy提供了preceding方法，创建的是OverWindowWithPreceding
- OverWindowWithPreceding则包含了partitionBy、orderBy、preceding属性，它提供了as方法创建OverWindow，另外还提供了following方法用于设置following offset
OverWindowedTable
flink-table_2.11-1.7.0-sources.jar!/org/apache/flink/table/api/table.scala
class OverWindowedTable(
private[flink] val table: Table,
private[flink] val overWindows: Array[OverWindow]) {
def select(fields: Expression*): Table = {
val expandedFields = expandProjectList(
fields,
table.logicalPlan,
table.tableEnv)
if(fields.exists(_.isInstanceOf[WindowProperty])){
throw new ValidationException(
"Window start and end properties are not available for Over windows.")
}
val expandedOverFields = resolveOverWindows(expandedFields, overWindows, table.tableEnv)
new Table(
table.tableEnv,
Project(
expandedOverFields.map(UnresolvedAlias),
table.logicalPlan,
// required for proper projection push down
explicitAlias = true)
.validate(table.tableEnv)
)
}
def select(fields: String): Table = {
val fieldExprs = ExpressionParser.parseExpressionList(fields)
//get the correct expression for AggFunctionCall
val withResolvedAggFunctionCall = fieldExprs.map(replaceAggFunctionCall(_, table.tableEnv))
select(withResolvedAggFunctionCall: _*)
}
}
- OverWindowedTable构造器需要overWindows参数；它只提供select操作，其中select可以接收String类型的参数，也可以接收Expression类型的参数；String类型的参数会被转换为Expression类型，最后调用的是Expression类型参数的select方法；select方法创建了新的Table，其Project的projectList为expandedOverFields.map(UnresolvedAlias)，而expandedOverFields则通过resolveOverWindows(expandedFields, overWindows, table.tableEnv)得到
小结
- Over Windows类似SQL的over子句，它可以基于event-time、processing-time或者row-count；具体可以通过Over类来构造，其中必须设置orderBy、preceding及as方法；它有Unbounded及Bounded两大类(
对于event-time及processing-time使用unbounded_range来表示Unbounded，对于row-count使用unbounded_row来表示Unbounded；对于event-time及processing-time使用诸如1.minutes来表示Bounded，对于row-count使用诸如10.rows来表示Bounded) - Table提供了OverWindow参数的window方法，用来进行Over Windows操作，它创建的是OverWindowedTable；OverWindow定义了alias、partitionBy、orderBy、preceding、following属性；Over类是创建over window的帮助类，它提供了orderBy及partitionBy两个方法，分别创建的是OverWindowWithOrderBy及PartitionedOver，而PartitionedOver提供了orderBy方法，创建的是OverWindowWithOrderBy；OverWindowWithOrderBy提供了preceding方法，创建的是OverWindowWithPreceding；OverWindowWithPreceding则包含了partitionBy、orderBy、preceding属性，它提供了as方法创建OverWindow，另外还提供了following方法用于设置following offset
- OverWindowedTable构造器需要overWindows参数；它只提供select操作，其中select可以接收String类型的参数，也可以接收Expression类型的参数；String类型的参数会被转换为Expression类型，最后调用的是Expression类型参数的select方法；select方法创建了新的Table，其Project的projectList为expandedOverFields.map(UnresolvedAlias)，而expandedOverFields则通过resolveOverWindows(expandedFields, overWindows, table.tableEnv)得到
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