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https://issues.apache.org/jira/browse/CALCITE-2302?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16912839#comment-16912839
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Danny Chan commented on CALCITE-2302:
-------------------------------------
For "9/2 returns 4.5", we indeed do the type coercion because we need to coerce
all the operands of "/" to double. So this change definitely belongs to the
implicit type coercion scope.
> 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: Critical
> Labels: pull-request-available
> Fix For: 1.21.0
>
> Time Spent: 7h 10m
> 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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