peter-toth opened a new pull request, #11265:
URL: https://github.com/apache/datafusion/pull/11265

   ## Which issue does this PR close?
   
   Part of https://github.com/apache/datafusion/issues/11194.
   
   ## Rationale for this change
   
   Curently `CommonSubexprEliminate` always skips expressions doesn't allow 
volatile expressions to be extracted, but this can be improved by allowing 
non-volatile subexpressions of volatile expressions to be extracted:
   
   I.e. from the plan:
   ```
   Projection (a + b) + rand() AS c1, (a + b) + rand() AS c2
   ```
   the expression `a + b` can be extracted as common expression despite the 
fact that `(a + b) + rand()` is volatile.
   
   ## What changes are included in this PR?
   
   Changes the rule to handle volatile expressions better by adding a new 
boolean flag to `VisitRecord::ExprItem` and propagating up volatility (validity 
for CSE).
   
   ## Are these changes tested?
   
   Yes, added new UT.
   
   ## Are there any user-facing changes?
   
   No.
   


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