Adez017 commented on code in PR #66:
URL: https://github.com/apache/datafusion-site/pull/66#discussion_r2029127026
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content/blog/2025-04-04-datafusion-userdefined-window-functions.md:
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+---
+layout: post
+title: User defined Window Functions in DataFusion
+date: 2025-04-04
+author: Aditya Singh Rathore
+categories: [tutorial]
+---
+
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+{% comment %}
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+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
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+{% endcomment %}
+-->
+
+## Introduction
+Window functions are a powerful feature in SQL, allowing for complex
analytical computations over a subset of data. However, efficiently
implementing them, especially sliding windows, can be quite challenging. With
DataFusion's recent support for user-defined window functions , developers now
have more flexibility and performance improvements at their disposal.
+
+In this post, we'll explore:
+
+- What window functions are and why they matter
+
+- Understanding sliding windows
+
+- The challenges of computing window aggregates efficiently
+
+- How DataFusion optimizes these computations
+
+- Alternative approaches and their trade-offs
+
+## Understanding Window Functions in SQL
+
+Imagine you're analyzing sales data and want insights without losing the finer
details. This is where **window functions** come into play. Unlike **GROUP
BY**, which condenses data, window functions let you retain each row while
performing calculations over a defined **range** —like having a moving lens
over your dataset.
+
+Picture a business tracking daily sales. They need a running total to
understand cumulative revenue trends without collapsing individual
transactions. SQL makes this easy:
+```sql
+SELECT id, value, SUM(value) OVER (ORDER BY id) AS running_total
+FROM sales;
+```
+This helps in analytical queries where we need cumulative sums, moving
averages, or ranking without losing individual records.
+
+
+## User Defined Window Functions
+
+Writing a user defined window function is slightly more complex than an
aggregate function due
+to the variety of ways that window functions are called. I recommend reviewing
the
+[online
documentation](https://datafusion.apache.org/library-user-guide/adding-udfs.html)
+for a description of which functions need to be implemented. The details of
how to implement
+these generally follow the same patterns as described above for aggregate
functions.
Review Comment:
I got your Point , and added the necessary changes required
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