kbendick commented on issue #5548:
URL: https://github.com/apache/iceberg/issues/5548#issuecomment-1217099105

   For the schema evolution, normally you should run the `ALTER TABLE ... ADD 
COLUMN` commands: 
https://iceberg.apache.org/docs/latest/spark-ddl/#alter-table--add-column
   
   If you want to have the schema updated during `merge into` without 
specifying it, you can use the `.option("mergeSchema", true)` when writing to 
the table.
   
   However, I'm not sure if that option is possible to use from SQL at the 
moment. We might need to capture the comments and apply them as hints (which 
isn't supported at this time afaik): 
https://spark.apache.org/docs/latest/sql-ref-syntax-qry-select-hints.html#hints
   
   For writes that can use the dataframe writer (which doesn't include `MERGE 
INTO` unfortunately), you could use the `mergeSchema` option and get the 
behavior you want.
   
   If you're interested in possibly getting the `mergeSchema` option as a hint, 
I would suggest opening a new feature request issue to request just that 
(linking to this one if you'd like). I'm not sure if it can be done, but as a 
feature request issue with a title like "Support Hints for Dataframe Writer 
Options Like 'mergeSchema'" and then explain your MERGE INTO case, that would 
be helpful.


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