Stamatis Zampetakis commented on CALCITE-2302:

Hey [~hyuan], it seems that you reviewed the PR; is it ready to go? Will it 
make it for 1.21.0?

> Implicit type cast support
> --------------------------
>                 Key: CALCITE-2302
>                 URL: https://issues.apache.org/jira/browse/CALCITE-2302
>             Project: Calcite
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 1.17.0
>            Reporter: Danny Chan
>            Assignee: Danny Chan
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.21.0
>          Time Spent: 4h 40m
>  Remaining Estimate: 0h
> Now many DBs have support implicit type cast, eg: SqlServer, Oracle, Hive.
> Implicit type cast is an useful function for many cases, So we should support 
> this.
> I checkout Calcite code and found that:
>  # Now we use a validator to validate our operands types[ through kinds of 
> namespaces and scopes ]
>  # Most of the validations will finally goes to
> {code:java}
> SqlOperator.validateOperands
> {code}
>  # which will use validation logic defined in corresponding 
> SqlOperandTypeChecker
> What i'm confused about is where should i put the implicit type cast logic 
> in? I figured out 2 ways:
>  # Supply a tool class/rules to add casts into a parsed SqlNode tree which 
> will then go through the validation logic later on.
>  # Unleash the validation logic in kinds of SqlOperandTypeChecker, then 
> modify the RelNode/RexNodes tree converted from a validated SqlNode tree to 
> add in casts through custom RelOptRules.
> So guys, which of the 2 ways should i go, or if there are better way to do 
> this?
> I need your help.
> Updated 18-05-30:
> Hi guys, i have made a PR in 
> [CALCITE-2302|https://github.com/apache/calcite/pull/706]
> This is design doc: [Calcite Implicit Type Cast 
> Design|https://docs.google.com/document/d/1g2RUnLXyp_LjUlO-wbblKuP5hqEu3a_2Mt2k4dh6RwU/edit?usp=sharing].
> This is the conversion types mapping: [Conversion Types 
> Mapping|https://docs.google.com/spreadsheets/d/1GhleX5h5W8-kJKh7NMJ4vtoE78pwfaZRJl88ULX_MgU/edit?usp=sharing].
> I really appreciate your suggestions, thx.

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