[GitHub] [pinot] walterddr commented on pull request #9385: Do not allow implicit cast between number, string, binary

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walterddr commented on PR #9385:
URL: https://github.com/apache/pinot/pull/9385#issuecomment-1247391278

   > Is there any reference available that talks about the restriction on implicit cast between them? If yes, can you link it to the description section of this PR?
   > 
   > We might need to carefully monitor the deployment in order to detect any existing use cases once this PR is merged.
   
   yes I was suggesting either a release note or a backward incompatible section in the PR but also in Pinot doc. 
   
   In terms of the rationale, AFAIK, 
   - nothing should be implicitly cast in logical plan. what we do NOW is b/c:
     - if a function expects `foo(int, long)` then they data type should be exact
     - however many system implements overload `foo(int, int), foo(int, long), foo(long, long) ...` so it will always find one properly. Pinot doesn't support these type of operator/function overloading thus we need to provide implicit cast.
   
   - many logical planner insert explicit CAST operator if the type doesn't match in user's provided SQL, for example:
     - `SELECT intCol + strCol FROM tbl` will result in a 
   ```
   LogicalProject(
     [+(intCol, CAST(strCol, INT))], 
     LogicalScan(
       tbl, 
       [intCol, strCol]
     )
   )
   ```
   
   so IMO as long as we state clearly in our user-facing implicit cast rule in doc we are good. I am incline to the following:
   - all numeric should have implicit cast and (1) throw exception (2) put MAX/MIN_VAL, or NaN when overflow
   - all DataType sharing the same StorageType should be able to implicitly cast between (for example JSON / STRING)
   - all other should not have default implicit cast rule
   - 
   
   


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