ISSUE:
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In end_write and end_write_group, Item_refs in having
conditions should refer to tmp_table->record[0]. But
join->ref_ptrs is not set to tmp_table->ref_array
because of this Item_refs in having is referring to Items
before tmp table. This lead to re-evaluation expressions
in having. Non-deterministic functions like rand() on
re-evaluation produces different results. If having refers
to one such expression in select list and it re-evaluate
them instead of referring to the saved results through
tmp_table->ref_array, can result in inconsistent results.
A similar issue in end_send where we need to refer to
grouping ref_array. Example: In loose index scan where
having refers to non-deterministic expression can result
in inconsistent results.

Solution:
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If there is no select distinct, convert having condition
to temp table conditions. With this Item_ref in having
will be converted to Item_field of temp field. Since
temp table already stores the result of group items, new
Item_fields will refer to these stored results now.

NOTE:
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1. We cannot set the join->ref_ptrs to tmp table ref_array
as in end_send_group, because this have impact on PREPARE
EXEC statements, reason is in JOIN::optimize we still do
resolution under the flag "first_optimization", here we try
to save select_lex->prep_where for next execution. Setting
ref_ptrs can make outer ref in where clause to point to
temp table items, so prep_where will point to some temp
table items, which will be freed after execution, for next
execution of same statement prep_where points to freed
items, then de-referencing same!!!.
This issue is solved with WL7082 in 5.7
2. If distinct is there I cannot move the having after
applying distinct reason is if having items of having
condition are not part of distinct then distinct key
may remove rows witch satisfy having and keep which
do not satisfy having. Thus me may loose some valid
rows before applying having.
3. If plan is loose index scan we do not fix it in 5.6
because to fix this in end_send we need to set
join->ref_ptrs to items3. As in point 1 doing any such
things in 5.6 will lead to crash for PS. Already we have
similar issue for end_send_group. so avoiding it.