eejbyfeldt opened a new issue, #13060:
URL: https://github.com/apache/datafusion/issues/13060
### Describe the bug
Currently we do not consider the volatility of expressions in
SimplifyExpressions. This leads us to doing rewrites that might change the
results and lead to unexpected behavior.
### To Reproduce
Consider the following query:
```
> explain select * from VALUES (1), (2) where random() = 0 OR (column1 = 2
AND random() = 0);
+---------------+---------------------------------------------+
| plan_type | plan |
+---------------+---------------------------------------------+
| logical_plan | Filter: random() = Float64(0) |
| | Values: (Int64(1)), (Int64(2)) |
| physical_plan | CoalesceBatchesExec: target_batch_size=8192 |
| | FilterExec: random() = 0 |
| | ValuesExec |
| | |
+---------------+---------------------------------------------+
2 row(s) fetched.
Elapsed 0.013 seconds.
```
The predicate get simplified into `random() = 0`
### Expected behavior
The predicate should not be simplified so we deduplicat the volatile
expressions.
```
> explain select * from VALUES (1), (2) where random() = 0 OR (column1 = 2
AND random() = 0);
+---------------+----------------------------------------------------------------------------------+
| plan_type | plan
|
+---------------+----------------------------------------------------------------------------------+
| logical_plan | Filter: random() = Float64(0) OR column1 = Int64(2) AND
random() = Float64(0) |
| | Values: (Int64(1)), (Int64(2))
|
| physical_plan | CoalesceBatchesExec: target_batch_size=8192
|
| | FilterExec: random() = 0
|
| | ValuesExec
|
| |
|
+---------------+----------------------------------------------------------------------------------+
2 row(s) fetched.
Elapsed 0.013 seconds.
random() = CAST(Int64(0) AS Float64) OR column1 = Int64(2) AND random() =
CAST(Int64(0) AS Float64)
```
### Additional context
We can not exclude volatile expressions outright from simplification as we
would still like the simplify for example following predicate
```
> explain select * from VALUES (1), (2) where column1 = 2 OR (column1 = 2
AND random() = 0);
+---------------+---------------------------------------------+
| plan_type | plan |
+---------------+---------------------------------------------+
| logical_plan | Filter: column1 = Int64(2) |
| | Values: (Int64(1)), (Int64(2)) |
| physical_plan | CoalesceBatchesExec: target_batch_size=8192 |
| | FilterExec: column1@0 = 2 |
| | ValuesExec |
| | |
+---------------+---------------------------------------------+
2 row(s) fetched.
Elapsed 0.015 seconds.
```
As it does not change the result.
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