maropu commented on a change in pull request #28121: [SPARK-31348][SQL][DOCS]
Document Join in SQL Reference
URL: https://github.com/apache/spark/pull/28121#discussion_r404458324
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File path: docs/sql-ref-syntax-qry-select-join.md
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@@ -18,5 +18,236 @@ license: |
See the License for the specific language governing permissions and
limitations under the License.
---
+### Description
-**This page is under construction**
+A SQL join is used to combine rows from two relations based on join criteria.
The following section describes the overall join syntax and the sub-sections
cover different types of joins along with examples.
+
+### Syntax
+{% highlight sql %}
+
+relation { [ join_type ] JOIN relation [ join_criteria ] | NATURAL join_type
JOIN relation }
+
+{% endhighlight %}
+
+### Parameters
+<dl>
+ <dt><code><em>relation</em></code></dt>
+ <dd>
+ Specifies the relation to be joined.
+ </dd>
+ <dt><code><em>join_type</em></code></dt>
+ <dd>
+ Specifies the join type.<br><br>
+ <b>Syntax:</b><br>
+ <code>
+ [ INNER ]
+ | CROSS
+ | LEFT [ OUTER ]
+ | [ LEFT ] SEMI
+ | RIGHT [ OUTER ]
+ | FULL [ OUTER ]
+ | [ LEFT ] ANTI
+ </code>
+ </dd>
+ <dt><code><em>join_criteria</em></code></dt>
+ <dd>
+ Specifies how the rows from one relation will be combined with the rows of
another relation.<br><br>
+ <b>Syntax:</b>
+ <code>
+ ON boolean_expression | USING ( column_name [ , column_name ... ] )
+ </code> <br><br>
+ <code>boolean_expression</code><br>
+ Specifies an expression with a return type of boolean.
Review comment:
nit: the format?
```
<dd>
Specifies how the rows from one relation will be combined with the rows
of another relation.<br><br>
<b>Syntax:</b>
<code>
ON boolean_expression | USING ( column_name [ , column_name ... ] )
</code> <br><br>
<code>boolean_expression</code><br>
Specifies an expression with a return type of boolean.
...
```
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