maropu commented on a change in pull request #28139: [SPARK-31362][SQL][DOCS]
Document Set Operators in SQL Reference
URL: https://github.com/apache/spark/pull/28139#discussion_r404465589
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File path: docs/sql-ref-syntax-qry-select-setops.md
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@@ -19,4 +19,125 @@ license: |
limitations under the License.
---
-**This page is under construction**
+Set operators are used to combine the results of two queries into a single
result. Spark SQL supports three types of set operators:
+- `EXCEPT` and `EXCEPT ALL`
+- `INTERSECT` and `INTERSECT ALL`
+- `UNION` and `UNION ALL`
+
+Note that the queries' result sets must have the same number of columns and
compatible data types for the respective columns.
+
+### EXCEPT and EXCEPT ALL
+`EXCEPT` and `EXCEPT ALL` return the rows that are found in one query but not
the other query. `EXCEPT` takes only distinct rows while `EXCEPT ALL` does not
remove duplicates.
+
+#### Syntax
+{% highlight sql %}
+[ ( ] query [ ) ] EXCEPT [ ALL ] [ ( ] query[ ) ]
+{% endhighlight %}
+
+### INTERSECT and INTERSECT ALL
+`INTERSECT` and `INTERSECT ALL` return the rows that are found in both
queries. `INTERSECT` takes only distinct rows while `INTERSECT ALL` does not
remove duplicates.
+
+#### Syntax
+{% highlight sql %}
+[ ( ] query [ ) ] INTERSECT [ ALL ] [ ( ] query [ ) ]
+{% endhighlight %}
+
+### UNION and UNION ALL
+`UNION` and `UNION ALL` return the rows that are found in either query.
`UNION` takes only distinct rows while `UNION ALL` does not remove duplicates.
+
+#### Syntax
+{% highlight sql %}
+[ ( ] query [ ) ] UNION [ ALL ] [ ( ] query [ ) ]
+{% endhighlight %}
+
+### Examples
+{% highlight sql %}
+-- Use number1 and number2 tables to demonstrate set operators.
+SELECT * FROM number1;
++---+
+| C|
Review comment:
super nit though... could the column name be lowercased for distinguishing
it from the SQL keywords?
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