pengzhiwei2018 edited a comment on pull request #2645:
URL: https://github.com/apache/hudi/pull/2645#issuecomment-803355840
> Getting started on this. Sorry for the delay.
>
> How important are the changes around writeSchema vs inputSchema and such
changes to the SQL implementation?
Hi @vinothchandar ,Thanks for your review.
It's necessary to introduce the `inputSchema` & `tableSchema` to replace the
origin `writeSchema` for MergeInto.
For example:
```
Merge Into h0 using (
select id, name, flag from s) as s0
on s0.id = h0.id
when matched and flag ='u' then update set id = s0.name, name = s0.name
when not matched then insert (id, name) values(s0.id, s0.name)
```
The input is `"select id, name, flag from s"` which schema is `(id, name,
flag)`. But the record write to the table is `(id, name) ` after the
update&insert translate. The inputSchema is not equal to the writeSchema. So
the origin `writeSchema` can not satisfy this scenario.
I introduce introduce the `inputSchema` & `tableSchema` to solve this
problem. The `inputSchema` is used to parse the incoming record and the
`tableSchema` for write & read record from the table.
In most case except the MergeInto, The `inputSchema` is the same the
`tableSchema`,So it should not affect the origin logical, IMO.
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