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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-4469) Add support for user defined table function in Table API & SQL
Date Fri, 04 Nov 2016 15:17:59 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4469?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15636650#comment-15636650
] 

ASF GitHub Bot commented on FLINK-4469:
---------------------------------------

Github user sunjincheng121 commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2653#discussion_r86557493
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/TableEnvironment.scala
---
    @@ -152,21 +153,40 @@ abstract class TableEnvironment(val config: TableConfig) {
       protected def getBuiltInRuleSet: RuleSet
     
       /**
    -    * Registers a [[UserDefinedFunction]] under a unique name. Replaces already existing
    +    * Registers a [[ScalarFunction]] under a unique name. Replaces already existing
         * user-defined functions under this name.
         */
    -  def registerFunction(name: String, function: UserDefinedFunction): Unit = {
    -    function match {
    -      case sf: ScalarFunction =>
    -        // register in Table API
    -        functionCatalog.registerFunction(name, function.getClass)
    +  def registerFunction(name: String, function: ScalarFunction): Unit = {
    +    // register in Table API
    +    functionCatalog.registerFunction(name, function.getClass)
     
    -        // register in SQL API
    -        functionCatalog.registerSqlFunction(sf.getSqlFunction(name, typeFactory))
    +    // register in SQL API
    +    functionCatalog.registerSqlFunction(function.getSqlFunction(name, typeFactory))
    +  }
    +
    +  /**
    +    * Registers a [[TableFunction]] under a unique name. Replaces already existing
    +    * user-defined functions under this name.
    +    */
    +  private[flink] def registerTableFunctionInternal[T: TypeInformation](
    +    name: String, tf: TableFunction[T]): Unit = {
     
    -      case _ =>
    -        throw new TableException("Unsupported user-defined function type.")
    +    val typeInfo: TypeInformation[_] = if (tf.getResultType != null) {
    +      tf.getResultType
    +    } else {
    +      implicitly[TypeInformation[T]]
         }
    +
    +    val (fieldNames, fieldIndexes) = UserDefinedFunctionUtils.getFieldInfo(typeInfo)
    --- End diff --
    
    For the sake of simplicity, is it possible to encapsulate a ”createSqlFunctions“ method
in tablefunciton? 


> 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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