e-dard opened a new issue #408:
URL: https://github.com/apache/arrow-datafusion/issues/408
**Describe the bug**
If you run a `LogicalPlan` that has a `TableProviderFilterPushDown`
`TableProvider`, then the filter pushdown optimiser rule will keep adding
filters to the pushed down table scan without checking if they're already
present.
Given the plan:
```
Filter: #a Eq Int64(1)
TableScan: projection=None
```
it will be optimised to the following plan the first time it runs through
the filter:
```
Filter: #a Eq Int64(1)
TableScan: projection=None, filters=[#a Eq Int64(1)]
```
If you run it through the optimiser again then it will not be left as is.
Instead it will become:
```
Filter: #a Eq Int64(1)
TableScan: projection=None, filters=[#a Eq Int64(1), #a Eq Int64(1)]
```
**To Reproduce**
Run a logical plan that pushes predicates down to the table provider through
the plan optimiser twice. All pushed down expression filters will be duplicated
in the table scan filters.
**Expected behavior**
The plan should not change if it's ran through the optimiser multiple times.
**Additional context**
Whilst the current behaviour produces correct plans they are not optimal
because they can contain redunant duplicate filters if they're run through the
optimiser multiple times.
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