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Bug#50539: Wrong result when loose index scan is used for an aggregate

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function with distinct.
Loose index scan is used to find MIN/MAX values using appropriate index and
thus allow to avoid grouping. For each found row it updates non-aggregated
fields with values from row with found MIN/MAX value.
Without loose index scan non-aggregated fields are copied by end_send_group
function. With loose index scan there is no need in end_send_group and
end_send is used instead. Non-aggregated fields still need to be copied and
this was wrongly implemented in QUICK_GROUP_MIN_MAX_SELECT::get_next.
WL#3220 added a case when loose index scan can be used with end_send_group to
optimize calculation of aggregate functions with distinct. In this case
the row found by QUICK_GROUP_MIN_MAX_SELECT::get_next might belong to a next
group and copying it will produce wrong result.

Update of non-aggregated fields is moved to the end_send function from
QUICK_GROUP_MIN_MAX_SELECT::get_next.
This commit is contained in:
Evgeny Potemkin
2010-02-12 11:51:52 +03:00
parent 6bad45745c
commit b5f40f3454
4 changed files with 50 additions and 14 deletions
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6
sql/sql_select.cc
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@ -12255,6 +12255,12 @@ end_send(JOIN *join, JOIN_TAB *join_tab __attribute__((unused)),
if (!end_of_records)
{
int error;
if (join->tables &&
join->join_tab->is_using_loose_index_scan())
{
/* Copy non-aggregated fields when loose index scan is used. */
copy_fields(&join->tmp_table_param);
}
if (join->having && join->having->val_int() == 0)
DBUG_RETURN(NESTED_LOOP_OK); // Didn't match having
error=0;