xianyinxin opened a new pull request #28875:
URL: https://github.com/apache/spark/pull/28875
### What changes were proposed in this pull request?
This PR add unlimited MATCHED and NOT MATCHED clauses in MERGE INTO
statement.
### Why are the changes needed?
Now the MERGE INTO syntax is,
```
MERGE INTO [db_name.]target_table [AS target_alias]
USING [db_name.]source_table [<time_travel_version>] [AS source_alias]
ON <merge_condition>
[ WHEN MATCHED [ AND <condition> ] THEN <matched_action> ]
[ WHEN MATCHED [ AND <condition> ] THEN <matched_action> ]
[ WHEN NOT MATCHED [ AND <condition> ] THEN <not_matched_action> ]
```
It would be nice if we support unlimited MATCHED and NOT MATCHED clauses in
MERGE INTO statement, because users may want to deal with different "AND
<condition>"s, the result of which just like a series of "CASE WHEN"s. The
expected syntax looks like
```
MERGE INTO [db_name.]target_table [AS target_alias]
USING [db_name.]source_table [<time_travel_version>] [AS source_alias]
ON <merge_condition>
[when_clause [, ...]]
```
where when_clause is
```
WHEN MATCHED [ AND <condition> ] THEN <matched_action>
```
or
```
WHEN NOT MATCHED [ AND <condition> ] THEN <not_matched_action>
```
### Does this PR introduce _any_ user-facing change?
Yes. The SQL command changes, but it is backward compatible.
### How was this patch tested?
New tests added.
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