planbuilder: use OR for not in comparisons

[systay]

Description

The plans produced for NOT IN queries that have to be scattered did not handle the missing values case, which leads to wrong results for these situations.

Related Issue(s)

Fixes #14605

Checklist0

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[vitess-bot]

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[arthurschreiber]

😢

[wangweicugw]

I have a question. It seems that in this scenario, we can remove the "not :__sq_has_values" condition. Why do we need to convert it to "or"?

[systay]

Excellent question!

We have already built the queries by this time, so we need to be able to send down something that is valid SQL.
NOT IN () does not even parse - we need to have at least one value there.
We can't stick NULL there, NOT IN (NULL) evaluates to NULL, not true.
We just put in the fake value 0. Just to make sure that we end up with true for the empty results, even if the column we are comparing against does contain a 0, we add this not :__sq_has_values that will return true no matter what.

[systay]

If it is important, we would need to come up with a value that we put into the ::__sq1 tuple that guarantees that id not in ::__sq1 returns true for all values of id. We can make it very unlikely, but not guarantee that we will no clash, right?