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https://issues.apache.org/jira/browse/FLINK-3754?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15278169#comment-15278169
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ASF GitHub Bot commented on FLINK-3754:
---------------------------------------

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

    https://github.com/apache/flink/pull/1958#discussion_r62681024
  
    --- Diff: 
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/expressions/Expression.scala
 ---
    @@ -17,13 +17,34 @@
      */
     package org.apache.flink.api.table.expressions
     
    -import java.util.concurrent.atomic.AtomicInteger
    -
     import org.apache.calcite.rex.RexNode
     import org.apache.calcite.tools.RelBuilder
     
    -abstract class Expression extends TreeNode[Expression] { self: Product =>
    -  def name: String = Expression.freshName("expression")
    +import org.apache.flink.api.common.typeinfo.TypeInformation
    +import org.apache.flink.api.table.trees.TreeNode
    +import org.apache.flink.api.table.validate.ExprValidationResult
    +
    +abstract class Expression extends TreeNode[Expression] {
    +  /**
    +    * Returns the [[TypeInformation]] for evaluating this expression.
    +    * It is sometimes not available until the expression is valid.
    +    */
    +  def dataType: TypeInformation[_]
    --- End diff --
    
    can we rename this field to `resultType`?


> Add a validation phase before construct RelNode using TableAPI
> --------------------------------------------------------------
>
>                 Key: FLINK-3754
>                 URL: https://issues.apache.org/jira/browse/FLINK-3754
>             Project: Flink
>          Issue Type: Improvement
>          Components: Table API
>    Affects Versions: 1.0.0
>            Reporter: Yijie Shen
>            Assignee: Yijie Shen
>
> Unlike sql string's execution, which have a separate validation phase before 
> RelNode construction, Table API lacks the counterparts and the validation is 
> scattered in many places.
> I suggest to add a single validation phase and detect problems as early as 
> possible.



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