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Fix issues due to mask aliasing #15680

Merged
merged 2 commits into from
Jan 17, 2023
Merged

Fix issues due to mask aliasing #15680

merged 2 commits into from
Jan 17, 2023

Commits on Jan 17, 2023

  1. Disallow multiple masks on a given column 

    This is problematic because:
* There is no guarantee about the ordering of application of masks,
  which could result in non-deterministic results at best or
  query failures in the worst case
* Allowing multiple masks, especially when provided by different
  connectors, means that one cannot reason about a mask expression
  in isolation with respect to the input the expression expects.
    @martint
    martint committed Jan 17, 2023
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  2. Fix aliasing of fields in mask expressions 

    This causes two problems:
* Masks can inadvertently refer to columns that appear earlier
  in the list of columns as the projection is planned. This
  causes the mask expression to see the masked value of other columns
  instead of the underlying value
* A possible bug in other optimizers causes mask expressions to be
  lost when the result of a such an expression is of type ROW
  and there's a dereference of a field downstream
    @martint
    martint committed Jan 17, 2023
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