Distinct and order by with different columns about clickhouse HOT 4 CLOSED

There are two possibilities:

• document that it is implementation specific behavior;
• throw an exception (and document this behavior).

I like second variant, but first is more free. Because it is sometimes usable, and also it could be correct (well specified) in subset of cases.

By the way, it is impossible to specify clear semantic (distinct after order or distinct before order) when doing ORDER BY and DISTINCT by different columns, because in query execution pipeline, there are 'partial sorting' and 'partial distinct' steps, which could be interleaved.

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@BayoNet ???

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There is one more argument that we should throw an exception: #15249

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@alexey-milovidov The documentation was updated.

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