hililiwei commented on PR #5585:
URL: https://github.com/apache/iceberg/pull/5585#issuecomment-1221714082

   > @hililiwei, we want to introduce standard syntax for this to avoid 
divergence across engines:
   > 
   > ```sql
   > -- Read from a branch
   > SELECT * FROM table BRANCH branch_name
   > -- Insert into a branch
   > INSERT INTO table BRANCH branch_name SELECT ...
   > -- Merge into a branch
   > MERGE INTO table BRANCH branch_name USING ...
   > -- Read from a tag
   > SELECT * FROM table AT TAG tag_name
   > ```
   > 
   > It's very unlikely that other engines will support the multipart 
identifier syntax. Right now, I think we should focus on getting dataframe 
operations working and then move on to SQL after that.
   
   Thank you for your answer. This syntax appears to need to wait for engine 
support. Or rewrite the engine's syntax file in the iceberg, as hudi did in 
spark 3.2 to support time travel. Otherwise, we don't seem to be able to use it 
in an earlier version of the engine. Of course, we can customize the engine's 
code and use it internally, but that's not realistic for a lot of tech teams, 
who tend to prefer out-of-the-box.
   
   I don't know if that's the case with other teams, but we're more 
conservative in upgrading engine versions, for example, we're still using Spark 
3.1 on a large scale. (That's why I raised a lot of PRs for reverse port of 
code to Spark3.1) , and use it for a long foreseeable period of time because we 
made a lot of internal changes to it and the upgrade wasn't that easy. This 
could cause us to be unavailable for a short period of time even if the engine 
supports it.
   
   But no matter what, thanks again for your answer, I will remove it from this 
PR and keep only the option part.
   
   Thank you very much.
   Liwei


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