drin commented on PR #20059:
URL: https://github.com/apache/datafusion/pull/20059#issuecomment-4034120420
@alamb it was a misunderstanding on my part. I thought that preimage would
transform any expression of the form `fn(x) <op> <constant>` by transforming
the `constant` using a range of equivalent inputs ("the interval") for
comparison. For example, if `N` is `2`, then its equivalent interval for
`floor(x)` would be `[2, 3)`. Then, `floor(x) <op> 2` could be rewritten as `x`
and some comparison with `[2, 3)`. Similarly for `floor(x) <op> 2.8`.
However, for `floor(x)`, the actual preimage implementation only considers
the lower bound. For the same example, where `N` is some constant in the range
`[2, 3)`, only `2` is considered for the rewrite, thus: `x < 2`, or `x <= 2`,
or `x >= 2 and x < 3`.
Based on the discussion in #18648 , the current implementation works as
expected and if the constant is some value in the range `(2, 3)` it will remain
in the expression to be evaluated in the usual way. For example, `floor(x) =
2.8` does not get simplified to `false`, it remains in the predicate to be
evaluated as usual.
My comments here can be ignored and I will address them in a follow-up PR
that expands the preimage simplification.
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