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https://issues.apache.org/jira/browse/FLINK-3754?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15253874#comment-15253874
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ASF GitHub Bot commented on FLINK-3754:
---------------------------------------
Github user yjshen commented on the pull request:
https://github.com/apache/flink/pull/1916#issuecomment-213419043
The type annotation work is done from bottom to top:
Firstly, we know each schema of the two input, and we know `List[]
expression` in `Project` are used to manipulate one row of table data as input
and output one value per expression, therefore, we can infer the the output
schema of `Project` (in the current impl this was expressed as: `def output:
Seq[Attribute]`) if we know each expressions `dataType`.
For example, `Add`'s dataType is same as it's input, `Or`'s dataType is
always `Boolean`, `pow(a, b)`'s dataType is always `Double`, however, if and
only if we understand all kinds of expressions, we are able to infer its
`dataType`. The main problems here is we only have `Call`(Unresolved Function)
generated during expression construction, therefore, we should resolve them
first into solid `Expression`s. `FunctionCatalog` is introduced here for a
mapping from `FunctionName -> Expression`, we can easily finish the translation
work as we look up `catalog`.
> 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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