> ## Documentation Index
> Fetch the complete documentation index at: https://docs.risingwave.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Streaming optimizations

> Learn about how to improve the performance of streaming queries by rewriting them using specific patterns.

This section covers best practices for optimizing streaming queries.
You can often achieve better performance by rewriting your SQL to follow certain recommended patterns.

## SQL optimizations

### UNION vs UNION ALL

UNION removes duplicates, while UNION ALL does not.
If you know that your data does not contain duplicates, use UNION ALL to avoid the overhead of duplicate removal.
Alternatively, if the duplicate set is small, you can also filter out duplicates when querying the result set.

### OverWindow vs GroupTopN

OverWindow is a streaming operator that maintains the state of the window and computes the row number for each row in the partition.

Queries look something like:

```sql theme={null}
select *, row_number() over (PARTITION BY v1 order by v2) r from t3
```

This can be optimized by using the `GroupTopN` operator instead.

Checkout [Converting StreamOverWindow to StreamGroupTopN](/processing/sql/top-n-by-group#converting-streamoverwindow-to-streamgrouptopn) for more details.

## Join optimizations

Checkout [Join Optimizations](/processing/sql/joins#converting-dimension-table-joins-to-process-time-joins) for more details.