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https://issues.apache.org/jira/browse/FLINK-4469?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15711936#comment-15711936
]
ASF GitHub Bot commented on FLINK-4469:
---------------------------------------
Github user twalthr commented on a diff in the pull request:
https://github.com/apache/flink/pull/2653#discussion_r90419246
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/functions/TableFunction.scala
---
@@ -0,0 +1,121 @@
+/*
+ * 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.api.table.functions
+
+import java.util
+
+import org.apache.flink.api.common.functions.InvalidTypesException
+import org.apache.flink.api.common.typeinfo.TypeInformation
+import org.apache.flink.api.java.typeutils.TypeExtractor
+import org.apache.flink.api.table.ValidationException
+
+/**
+ * Base class for a user-defined table function (UDTF). A user-defined
table functions works on
+ * zero, one, or multiple scalar values as input and returns multiple
rows as output.
+ *
+ * The behavior of a [[TableFunction]] can be defined by implementing a
custom evaluation
+ * method. An evaluation method must be declared publicly and named
"eval". Evaluation methods
+ * can also be overloaded by implementing multiple methods named "eval".
+ *
+ * User-defined functions must have a default constructor and must be
instantiable during runtime.
+ *
+ * By default the result type of an evaluation method is determined by
Flink's type extraction
+ * facilities. This is sufficient for basic types or simple POJOs but
might be wrong for more
+ * complex, custom, or composite types. In these cases
[[TypeInformation]] of the result type
+ * can be manually defined by overriding [[getResultType()]].
+ *
+ * Internally, the Table/SQL API code generation works with primitive
values as much as possible.
+ * If a user-defined table function should not introduce much overhead
during runtime, it is
+ * recommended to declare parameters and result types as primitive types
instead of their boxed
+ * classes. DATE/TIME is equal to int, TIMESTAMP is equal to long.
+ *
+ * Example:
+ *
+ * {{{
+ *
+ * public class Split extends TableFunction<String> {
+ *
+ * // implement an "eval" method with several parameters you want
+ * public void eval(String str) {
+ * for (String s : str.split(" ")) {
+ * collect(s); // use collect(...) to emit an output row
+ * }
+ * }
+ *
+ * // can overloading eval method here ...
+ * }
+ *
+ * val tEnv: TableEnvironment = ...
+ * val table: Table = ... // schema: [a: String]
+ *
+ * // for Scala users
+ * val split = new Split()
+ * table.crossApply(split('c) as ('s)).select('a, 's)
+ *
+ * // for Java users
+ * tEnv.registerFunction("split", new Split()) // register table
function first
+ * table.crossApply("split(a) as (s)").select("a, s")
+ *
+ * // for SQL users
+ * tEnv.registerFunction("split", new Split()) // register table
function first
+ * tEnv.sql("SELECT a, s FROM MyTable, LATERAL TABLE(split(a)) as T(s)")
+ *
+ * }}}
+ *
+ * @tparam T The type of the output row
+ */
+abstract class TableFunction[T] {
+
+ private val rows: util.ArrayList[T] = new util.ArrayList[T]()
+
+ /**
+ * Emit an output row.
+ *
+ * @param row the output row
+ */
+ protected def collect(row: T): Unit = {
+ // cache rows for now, maybe immediately process them further
+ rows.add(row)
+ }
+
+ /**
+ * Internal use. Get an iterator of the buffered rows.
+ */
+ def getRowsIterator = rows.iterator()
+
+ /**
+ * Internal use. Clear buffered rows.
+ */
+ def clear() = rows.clear()
+
+ //
----------------------------------------------------------------------------------------------
+
+ /**
+ * Returns the result type of the evaluation method with a given
signature.
+ *
+ * This method needs to be overriden in case Flink's type extraction
facilities are not
+ * sufficient to extract the [[TypeInformation]] based on the return
type of the evaluation
+ * method. Flink's type extraction facilities can handle basic types or
+ * simple POJOs but might be wrong for more complex, custom, or
composite types.
+ *
+ * @return [[TypeInformation]] of result type or null if Flink should
determine the type
+ */
+ def getResultType: TypeInformation[T] = null
--- End diff --
`ScalarFunction` has `getParameterTypes()` to be overridden if the
parameter types of the `eval` method can not be determined automatically. This
is missing in this class.
> Add support for user defined table function in Table API & SQL
> --------------------------------------------------------------
>
> Key: FLINK-4469
> URL: https://issues.apache.org/jira/browse/FLINK-4469
> Project: Flink
> Issue Type: New Feature
> Components: Table API & SQL
> Reporter: Jark Wu
> Assignee: Jark Wu
>
> Normal user-defined functions, such as concat(), take in a single input row
> and output a single output row. In contrast, table-generating functions
> transform a single input row to multiple output rows. It is very useful in
> some cases, such as look up in HBase by rowkey and return one or more rows.
> Adding a user defined table function should:
> 1. inherit from UDTF class with specific generic type T
> 2. define one or more evel function.
> NOTE:
> 1. the eval method must be public and non-static.
> 2. the generic type T is the row type returned by table function. Because of
> Java type erasure, we can’t extract T from the Iterable.
> 3. use {{collect(T)}} to emit table row
> 4. eval method can be overload. Blink will choose the best match eval method
> to call according to parameter types and number.
> {code}
> public class Word {
> public String word;
> public Integer length;
> }
> public class SplitStringUDTF extends UDTF<Word> {
> public Iterable<Word> eval(String str) {
> if (str != null) {
> for (String s : str.split(",")) {
> collect(new Word(s, s.length()));
> }
> }
> }
> }
> // in SQL
> tableEnv.registerFunction("split", new SplitStringUDTF())
> tableEnv.sql("SELECT a, b, t.* FROM MyTable, LATERAL TABLE(split(c)) AS
> t(w,l)")
> // in Java Table API
> tableEnv.registerFunction("split", new SplitStringUDTF())
> // rename split table columns to “w” and “l”
> table.crossApply("split(c) as (w, l)")
> .select("a, b, w, l")
> // without renaming, we will use the origin field names in the POJO/case/...
> table.crossApply("split(c)")
> .select("a, b, word, length")
> // in Scala Table API
> val split = new SplitStringUDTF()
> table.crossApply(split('c) as ('w, 'l))
> .select('a, 'b, 'w, 'l)
> // outerApply for outer join to a UDTF
> table.outerApply(split('c))
> .select('a, 'b, 'word, 'length)
> {code}
> See [1] for more information about UDTF design.
> [1]
> https://docs.google.com/document/d/15iVc1781dxYWm3loVQlESYvMAxEzbbuVFPZWBYuY1Ek/edit#
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