| /* |
| * 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.api.functions |
| |
| import org.apache.flink.table.api.types.InternalType |
| import org.apache.flink.table.expressions.{Expression, UnresolvedAggBufferReference, UnresolvedFieldReference} |
| |
| /** |
| * API for aggregation functions that are expressed in terms of expressions. |
| * |
| * When implementing a new expression-based aggregate function, you should first decide how many |
| * operands your function will have by implementing `inputCount` method. And then you can use |
| * `operands` fields to represent your operand, like `operands(0)`, `operands(2)`. |
| * |
| * Then you should declare all your buffer attributes by implementing `aggBufferAttributes`. You |
| * should declare all buffer attributes as `UnresolvedAggBufferReference`, and make sure the name |
| * of your attributes are unique within the function. You can then use these attributes when |
| * defining `initialValuesExpressions`, `accumulateExpressions`, `mergeExpressions` and |
| * `getValueExpression`. |
| * |
| * See an full example: [[org.apache.flink.table.codegen.expr.AvgAggFunction]] |
| */ |
| trait DeclarativeAggregateFunction extends UserDefinedFunction { |
| |
| /** |
| * How many inputs your function will deal with. |
| */ |
| def inputCount: Int |
| |
| /** |
| * All fields of the aggregate buffer. |
| */ |
| def aggBufferAttributes: Seq[UnresolvedAggBufferReference] |
| |
| /** |
| * The result type of the function |
| */ |
| def getResultType: InternalType |
| |
| /** |
| * Expressions for initializing empty aggregation buffers. |
| */ |
| def initialValuesExpressions: Seq[Expression] |
| |
| /** |
| * Expressions for accumulating the mutable aggregation buffer based on an input row. |
| */ |
| def accumulateExpressions: Seq[Expression] |
| |
| /** |
| * Expressions for retracting the mutable aggregation buffer based on an input row. |
| */ |
| def retractExpressions: Seq[Expression] = ??? |
| |
| /** |
| * A sequence of expressions for merging two aggregation buffers together. When defining these |
| * expressions, you can use the syntax `attributeName.left` and `attributeName.right` to refer |
| * to the attributes corresponding to each of the buffers being merged (this magic is enabled |
| * by the [[RichAggregateBufferAttribute]] implicit class). |
| */ |
| def mergeExpressions: Seq[Expression] |
| |
| /** |
| * An expression which returns the final value for this aggregate function. |
| */ |
| def getValueExpression: Expression |
| |
| /** |
| * A helper class for representing an attribute used in merging two |
| * aggregation buffers. When merging two buffers, `bufferLeft` and `bufferRight`, |
| * we merge buffer values and then update bufferLeft. |
| */ |
| implicit class RichAggregateBufferAttribute(a: UnresolvedAggBufferReference) { |
| /** Represents this attribute at the aggregate buffer side. */ |
| def left: UnresolvedAggBufferReference = a |
| |
| /** Represents this attribute at the input side. */ |
| def right: UnresolvedFieldReference = inputAggBufferAttributes(aggBufferAttributes.indexOf(a)) |
| } |
| |
| final val operands: Array[UnresolvedFieldReference] = { |
| require(inputCount >= 0, "inputCount must be greater than or equal to 0.") |
| (0 until inputCount).map { index => UnresolvedFieldReference(index.toString) }.toArray |
| } |
| |
| final val aggBufferSchema: Seq[InternalType] = aggBufferAttributes.map(_.resultType) |
| |
| final val inputAggBufferAttributes: Seq[UnresolvedFieldReference] = { |
| aggBufferAttributes.indices.map { index => UnresolvedFieldReference(index.toString) } |
| } |
| |
| } |