Fix-up for commit 476b24d084
Author: Monty
Date: Thu Feb 16 14:19:33 2023 +0200
MDEV-20057 Distinct SUM on CROSS JOIN and grouped returns wrong result
which misses initializing of sorder->suffix_length.
In this commit the initialization is implemented by passing
MY_ZEROFILL flag to the allocation of SORT_FIELD elements
SELECT DISTINCT did not work with expressions with sum functions.
Distinct was only done on the values stored in the intermediate temporary
tables, which only stored the value of each sum function.
In other words:
SELECT DISTINCT sum(a),sum(b),avg(c) ... worked.
SELECT DISTINCT sum(a),sum(b) > 2,sum(c)+sum(d) would not work.
The later query would do ONLY apply distinct on the sum(a) part.
Reviewer: Sergei Petrunia <sergey@mariadb.com>
This was fixed by extending remove_dup_with_hash_index() and
remove_dup_with_compare() to take into account the columns in the result
list that where not stored in the temporary table.
Note that in many cases the above dup removal functions are not used as
the optimizer may be able to either remove duplicates early or it will
discover that duplicate remove is not needed. The later happens for
example if the group by fields is part of the result.
Other things:
- Backported from 11.0 the change of Sort_param.tmp_buffer from char* to
String.
- Changed Type_handler::make_sort_key() to take String as a parameter
instead of Sort_param. This was done to allow make_sort_key() functions
to be reused by distinct elimination functions.
This makes Type_handler_string_result::make_sort_key() similar to code
in 11.0
- Simplied error handling in remove_dup_with_compare() to remove code
duplication.
