Is your feature request related to a problem?
This query

source = test |  eval b = a + 1 | sort b

is equivalent to:

source = test | sort a | eval b = a + 1

since a + 1 is monotonic and so it's collation equals to a.

We can transform the query into the latter one and then has chance to push down its sort into scan.

What solution would you like?
A clear and concise description of what you want to happen.

What alternatives have you considered?
A clear and concise description of any alternative solutions or features you've considered.

Do you have any additional context?
The SortProjectTransposeRule in Calcite doesn't support transpose a sort on RexCall.