HaoYang670 commented on issue #1727:
URL: 
https://github.com/apache/arrow-datafusion/issues/1727#issuecomment-1027559822


   Another that I find
   
https://github.com/apache/arrow-datafusion/blob/master/datafusion/src/optimizer/simplify_expressions.rs#L1042-L1054
   ```rust
           // volatile / stable functions should not be evaluated
           // rand() + (1 + 2) --> rand() + 3
           let fun = BuiltinScalarFunction::Random;
           assert_eq!(fun.volatility(), Volatility::Volatile);
           let rand = Expr::ScalarFunction { args: vec![], fun };
           let expr = rand.clone() + (lit(1) + lit(2));
           let expected = rand + lit(3);
           test_evaluate(expr, expected);
   
   
           // parenthesization matters: can't rewrite
           // (rand() + 1) + 2 --> (rand() + 1) + 2)
           let fun = BuiltinScalarFunction::Random;
           assert_eq!(fun.volatility(), Volatility::Volatile);
   ```
   
   We test `BuiltinScalarFunction::Random.volatility()` twice.


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