srowen commented on a change in pull request #27288: [SPARK-30579][DOC]
Document ORDER BY Clause of SELECT statement in SQL Reference
URL: https://github.com/apache/spark/pull/27288#discussion_r369608987
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File path: docs/sql-ref-syntax-qry-select-orderby.md
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@@ -18,5 +18,121 @@ license: |
See the License for the specific language governing permissions and
limitations under the License.
---
+The <code>ORDER BY</code> clause is used to return the result rows in a sorted
manner
+in the user specified order. Unlike the <code>SORT BY</code> clause, this
clause guarantees
+total order in the output.
-**This page is under construction**
+### Syntax
+{% highlight sql %}
+ORDER BY { expression [ sort_direction | nulls_sort_oder ] [ , ...] }
+{% endhighlight %}
+
+### Parameters
+<dl>
+ <dt><code><em>ORDER BY</em></code></dt>
+ <dd>
+ Specifies a comma-separated list of expressions along with optional
parameters <code>sort_direction</code>
+ and <code>nulls_sort_order</code> which are used to sort the rows.
+ </dd>
+ <dt><code><em>sort_direction</em></code></dt>
+ <dd>
+ Optionally specifies whether to sort the rows in ascending (lowest to
highest) or descending
+ (highest to lowest) order. The valid values for sort direction are
<code>ASC</code> for ascending
+ and <code>DESC</code> for descending. If sort direction is not explicitly
specified then by default
+ rows are sorted in ascending manner. <br><br>
+ <b>Syntax:</b>
+ <code>
+ [ ASC | DESC ]
+ </code>
+ </dd>
+ <dt><code><em>nulls_sort_order</em></code></dt>
+ <dd>
+ Optionally specifies whether NULL values are returned before/after
non-NULL values, based on the
+ sort direction. In Spark, NULL values are considered to be lower than any
non-NULL values by default.
+ Therefore the ordering of NULL values depend on the sort direction.<br><br>
+ <ol>
+ <li>If the sort order is ASC, NULLS are returned first; to force NULLS
to be last, use NULLS LAST</li>
Review comment:
I might turn this around, to emphasize the null sort order: "If `NULLS
FIRST` (the default), then NULLs are returned first if sort order is `ASC`, and
last if sort order is `DESC`" and likewise for the second items.
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