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[jira] [Created] (CALCITE-2302) Implicit type cast support

Yuzhao Chen created CALCITE-2302:

             Summary: Implicit type cast support
                 Key: CALCITE-2302
             Project: Calcite
          Issue Type: Improvement
          Components: core
    Affects Versions: 1.17.0
            Reporter: Yuzhao Chen
            Assignee: Julian Hyde
             Fix For: 1.17.0

Now many BDs 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 
# 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 ? There are several ways i figured out:
# 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.

So guys, i need your help, which of the 2 ways should i go, or if there are better way to do this?

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