Julian Hyde commented on CALCITE-2257:

For the expression {{x IS NOT NULL OR x IS NULL}} you will want to invoke 
simplify on the right-hand expression {{x IS NULL}} having created predicates 
for what you have learned from the left-hand expression. The RHS will only be 
invoked if {{x IS NULL}} is true.

This is extremely similar to what is needed to solve CALCITE-2247 (except OR 
rather than AND) so you should work with [~kgyrtkirk] and deliver a patch that 
solves both problems.

> Combination of predicates can be proved to be always true
> ---------------------------------------------------------
>                 Key: CALCITE-2257
>                 URL: https://issues.apache.org/jira/browse/CALCITE-2257
>             Project: Calcite
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 1.16.0
>            Reporter: Vitalii Diravka
>            Assignee: Vitalii Diravka
>            Priority: Major
>              Labels: filter
>             Fix For: 1.17.0
> I have found the case, when Filter operator is not necessary since filter 
> condition is always true, but that is not detected by current version of 
> Calcite.
> {code}
> select SAL from EMPNULLABLES_20 where SAL IS NOT NULL OR SAL is null
> {code}
> {code}
> LogicalProject(SAL=[$5])
>   LogicalFilter(condition=[OR(IS NOT NULL($5), IS NULL($5))])
>     LogicalProject(EMPNO=[$0], ENAME=[$1], JOB=[$2], MGR=[$3], HIREDATE=[$4], 
> SAL=[$5], COMM=[$6], SLACKER=[$8])
>       LogicalFilter(condition=[AND(=($7, 20), >($5, 1000))])
>         LogicalTableScan(table=[[CATALOG, SALES, EMPNULLABLES]])
> {code}
> But filter condition _OR(IS NOT NULL($5), IS NULL($5))_ can be proved to be 
> always true.
> I have tried _ReduceExpressionsRule_, but it doesn't give effect.

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