maropu commented on a change in pull request #28220: [SPARK-31390][SQL][DOCS]
Document Window Function in SQL Syntax Section
URL: https://github.com/apache/spark/pull/28220#discussion_r409242524
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File path: docs/sql-ref-syntax-qry-window.md
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@@ -19,4 +19,209 @@ license: |
limitations under the License.
---
-**This page is under construction**
+### Description
+
+Window functions operate on a group of rows, referred to as a window, and
calculate an aggregated value for each row based on the specified window.
Window functions are useful for processing tasks such as calculating a moving
average, computing a cumulative statistic, or accessing the value of rows given
the relative position of the current row.
+Spark SQL supports three types of window functions:
+
+ * Ranking Functions
+ * Analytic Functions
+ * Aggregate Functions
+
+### Syntax
+
+{% highlight sql %}
+window_function OVER ( [ partition_spec ] order_spec [ window_frame ] )
+{% endhighlight %}
+
+### Parameters
+
+<dl>
+ <dt><code><em>window_function</em></code></dt>
+ <dd>
+ <ul>
+ <li> Ranking Functions </li>
+ <br>
+ <b>Syntax:</b>
+ <code>
+ RANK | DENSE_RANK | PERCENT_RANK | NTILE | ROW_NUMBER
+ </code>
+ </ul>
+ <ul>
+ <li> Analytic Functions </li>
+ <br>
+ <b>Syntax:</b>
+ <code>
+ CUME_DIST | LAG | LEAD
+ </code>
+ </ul>
+ <ul>
+ <li> Aggregate Functions </li>
+ <br>
+ <b>Syntax:</b>
+ <code>
+ MAX | MIN | COUNT | SUM | AVG | ...
+ </code>
+ <br>
+ Please refer to the <a href="sql-ref-functions-builtin.html">Built-in
Function</a> document for a complete list of Spark aggregate functions.
+ </ul>
+ </dd>
+</dl>
+<dl>
+ <dt><code><em>partition_spec</em></code></dt>
+ <dd>
+ Specifies a comma separated list of key and value pairs for
partitions.<br><br>
+ <b>Syntax:</b><br>
+ <code>
+ { PARTITION | DISTRIBUTE } BY partition_col_name = partition_col_val (
[ , ... ] )
+ </code>
+ </dd>
+</dl>
+<dl>
+ <dt><code><em>order_spec</em></code></dt>
+ <dd>
+ Specifies an ordering of the rows.<br><br>
+ <b>Syntax:</b><br>
+ <code>
+ { ORDER | SORT } BY { expression [ ASC | DESC ] [ NULLS { FIRST | LAST
} ] [ , ... ] }
Review comment:
Could you move `ORDER BY` and `PARTITION BY` caluses into the `Syntax`
section like the Pg doc one?
```
[ existing_window_name ]
[ PARTITION BY expression [, ...] ]
[ ORDER BY expression [ ASC | DESC | USING operator ] [ NULLS { FIRST | LAST
} ] [, ...] ]
[ frame_clause ]
```
https://www.postgresql.org/docs/current/sql-select.html
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