Fix order by in case of sorting by primary key prefix and non primary key suffix.

[CurtizJ]

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• Bug Fix

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Fix ORDER BY in case of sorting by primary key prefix and non primary key suffix.

[akuzm]

I'm trying to figure out how this bug works:
With bug: input block streams sorted by A, (1) sort each block by AB, (2) merge streams as if sorted by A, (3) finish sorting the stream by AB as if the input stream is sorted by A (ok) and each block by AB <-- this last assumption is broken by merge.
With fix: input block streams sorted by A, merge streams as if sorted by A, sort each block by AB, finish sorting the stream by AB as if the input stream is sorted by A, and each block by AB -- all assumptions hold.
Is this correct?

As a side note, the names order_descr and sorting_info->prefix_order_desc make it impossible to tell which one is the input order and which is the required output order.

[CurtizJ]

Yes, you are right.

We can rename prefix_order_desc to read_order_descr or input_order_descr.

[akuzm]

Maybe something like input_order instead of sorting_info and output_order instead of order_descr?