[GitHub] [flink] Huanli-Meng commented on a change in pull request #12713: [FLINK-18254][doc] Add documentation for primary key syntax

[GitBox <gi...@apache.org>]

Huanli-Meng commented on a change in pull request #12713:
URL: https://github.com/apache/flink/pull/12713#discussion_r442794942



##########
File path: docs/dev/table/sql/create.md
##########
@@ -202,6 +209,39 @@ CREATE TABLE Orders (
 ) WITH ( . . . );
 {% endhighlight %}
 
+**PRIMARY KEY**
+
+Primary key constraint is a hint for Flink to leverage for optimizations. It tells that a column or a set of columns of a table or a view are unique and they **do not** contain null.
+Neither of columns in a primary can be nullable. Primary key therefore uniquely identify a row in a table.
+
+Primary key constraint can be either declared along with a column definition(a column constraint) or as a single line(a table constraint),

Review comment:
       ```suggestion
   Primary key constraint can be either declared along with a column definition (a column constraint) or as a single line(a table constraint),
   ```




----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.

For queries about this service, please contact Infrastructure at:
users@infra.apache.org