singhpk234 commented on code in PR #8094:
URL: https://github.com/apache/iceberg/pull/8094#discussion_r1266908612


##########
docs/spark-ddl.md:
##########
@@ -526,4 +531,4 @@ Tags can be removed via the `DROP TAG` sql
 
 ```sql
 ALTER TABLE prod.db.sample DROP TAG historical-tag
-```
\ No newline at end of file
+```

Review Comment:
   nit: is this required ? 



##########
docs/spark-ddl.md:
##########
@@ -306,12 +306,17 @@ ALTER TABLE prod.db.sample ALTER COLUMN col FIRST
 ALTER TABLE prod.db.sample ALTER COLUMN nested.col AFTER other_col
 ```
 
-Nullability can be changed using `SET NOT NULL` and `DROP NOT NULL`:
+Nullability for a non-nullable column can be changed using `DROP NOT NULL`:
 
 ```sql
 ALTER TABLE prod.db.sample ALTER COLUMN id DROP NOT NULL
 ```
 
+{{< hint info >}}
+It is not possible to change a nullable column to non-nullable with `SET NOT 
NULL` because Iceberg doesn't know whether there is existing data with null 
values.

Review Comment:
   [optional] 
   ```suggestion
   It is not possible to change a nullable column to a non-nullable column with 
`SET NOT NULL` because Iceberg doesn't know whether there is an existing data 
with null values.
   ```



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