xianyinxin commented on issue #26167: [SPARK-28893][SQL] Support MERGE INTO in 
the parser and add the corresponding logical plan
URL: https://github.com/apache/spark/pull/26167#issuecomment-549768500
 
 
   @cloud-fan , I have some doubts. As the doc in `ParsedStatement`, a 
`ParsedStatement` is not resolved because it need to be converted to concrete 
logical plan later.  For the currents statements, all of them are commands, 
which will be converted to `Command` after analyze phase, and the final command 
is resolved.
   
   To remove the redundant step that convert a logical plan to another form, I 
think a better choice is parse the sql to `MergeIntoTable` which is an 
unresolved command, and after analyzing, it becomes a resolved merge into 
command.
   
   However, I checked some other command like `CreateTable` in v1, it is parsed 
to a resolvable logical plan, and finally be converted to a concrete command 
like `CreateHiveTableAsSelectCommand` in analyze phase, the behaves of which is 
a little like the translation from `MergeIntoStatement` to `MergeIntoTable`. 
The different is, in the former,  converting `CreateTable` to 
`CreateHiveTableAsSelectCommand` is at the late period of analyze process, and 
converting ` MergeIntoStatement` to `MergeIntoTable` is at the beginning period 
of the analyze process.
    

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