InnoDB table, where all selected columns
belong to the same unique index key, returns
incorrect results
Server executes some queries via QUICK_GROUP_MIN_MAX_SELECT
(MIN/MAX optimization for queries with GROUP BY or DISTINCT
clause) and that optimization implies loose index scan, so all
grouping is done by the QUICK_GROUP_MIN_MAX_SELECT::get_next
method.
The server does not set the precomputed_group_by flag for some
QUICK_GROUP_MIN_MAX_SELECT queries and duplicates grouping by
call to the end_send_group function.
Fix: when the test_if_skip_sort_order function selects loose
index scan as a best way to satisfy an ORDER BY/GROUP BY type
of query, the precomputed_group_by flag has been set to use
end_send/end_write functions instead of end_send_group/
end_write_group functions.
