[GitHub] [spark] kevinyu98 commented on a change in pull request #27779: [SPARK-30962][SQL][DOC]Documentation for Alter table command phase 2

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kevinyu98 commented on a change in pull request #27779: [SPARK-30962][SQL][DOC]Documentation for Alter table command phase 2
URL: https://github.com/apache/spark/pull/27779#discussion_r389434757
 
 

 ##########
 File path: docs/sql-ref-syntax-ddl-alter-table.md
 ##########
 @@ -83,6 +82,108 @@ ALTER TABLE table_identifier ADD COLUMNS ( col_spec [ , col_spec ... ] )
 </dl>
 
 
+### ALTER OR CHANGE COLUMN
+`ALTER TABLE ALTER COLUMN` or `ALTER TABLE CHANGE COLUMN` statement changes column's comment.
+
+#### Syntax
+{% highlight sql %}
+ALTER TABLE table_identifier { ALTER | CHANGE } COLUMN col_spec alterColumnAction
+{% endhighlight %}
+
+#### Parameters
+<dl>
+  <dt><code><em>table_identifier</em></code></dt>
+  <dd>
+    Specifies a table name, which may be optionally qualified with a database name.<br><br>
+    <b>Syntax:</b>
+      <code>
+        [ database_name. ] table_name
+      </code>
+  </dd>
+</dl>
+
+<dl>
+  <dt><code><em>COLUMN col_spec</em></code></dt>
+  <dd>Specifies the columns to be altered to be changed.</dd>
+</dl>
+
+<dl>
+  <dt><code><em>alterColumnAction</em></code></dt>
+   <dd>
+     Change the comment string.<br><br>
 
 Review comment:
   I tested those: datatype, colPosition, set/drop not null, I got error which states v1 table can't do or only supported with v2 tables. So I didn't put those in the doc.

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