# Logical Transformation - Eliminate Outer Join and Predicates Push-Down Example
![`smart`](PredicatesPushDown_aa_002_20230922.png)
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Predicate push-down involves moving filtering conditions as close to the data source as possible (away from the TiDB server instance) to complete data filtering at an earlier stage. This approach reduces network traffic between the TiDB server and TiKV servers.

In the previous example, the left outer join is transformed into an inner join. As a result, the query can be optimized by applying the filter before the join operation, showcasing an instance of predicate push-down.  
- Since the join has already been transformed into an `INNER` join instead of an `OUTER` join, the filter `t2.val > 11` is applied before the join operation.  
- The filter `t2.val > 11` is executed at the TiKV layer rather than the TiDB layer.  

For more details, visit: [https://docs.pingcap.com/tidb/stable/predicate-push-down](https://docs.pingcap.com/tidb/stable/predicate-push-down).