[CALCITE-7301] Support unparse special syntax when operator is LAMBDA/MERGE/UNPIVOT

[dssysolyatin]

[dssysolyatin]

saw a useful comment from Julian on one of previous task:

It might be helpful for SqlUnparserTest to unparse everything before and after cloning. Could you enable that in this PR? Then you might not need a specific test case.

It would be good to add this to the current PR. Then we don't need such tests, I hope

[xiedeyantu]

So, is your PR intended to accomplish what Julian mentioned?

[dssysolyatin]

I added a test, but many operators in server package (ServerUnParserTest test) don’t have createCall. I’ll look into that next week.

Also, I’m not sure if I should add the operator at the end of getOperandList, or if I can reorder them to match the constructor parameter order. The last one would be much better. One example of this is UNPIVOT

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
95.0% Coverage on New Code
1.1% Duplication on New Code

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[mihaibudiu]

What is the status of this PR?

[dssysolyatin]

I will most likely come back to this PR at the end of next week