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Fixed bug#35844.

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The function test_if_skip_sort_order ignored any covering index used for ref
access of a table in a query with ORDER BY if this index was incompatible 
with the ORDER BY list and there was another covering index compatible with
this list. 
As a result sub-optimal execution plans were chosen for some queries with
ORDER BY clause.
This commit is contained in:
igor@olga.mysql.com
2008-04-22 21:49:39 -07:00
parent 013fd23675
commit b210e5df6d
4 changed files with 65 additions and 2 deletions
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7
sql/sql_select.cc
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@ -12966,6 +12966,7 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
uint tablenr= tab - join->join_tab;
ha_rows table_records= table->file->stats.records;
bool group= join->group && order == join->group_list;
ha_rows ref_key_quick_rows= HA_POS_ERROR;
LINT_INIT(best_key_parts);
LINT_INIT(best_key_direction);
LINT_INIT(best_records);
@ -12999,6 +13000,9 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
else
keys= usable_keys;
if (ref_key >= 0 && table->covering_keys.is_set(ref_key))
ref_key_quick_rows= table->quick_rows[ref_key];
read_time= join->best_positions[tablenr].read_time;
for (uint i= tablenr+1; i < join->tables; i++)
fanout*= join->best_positions[i].records_read; // fanout is always >= 1
@ -13093,7 +13097,8 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
index_scan_time < read_time)
{
ha_rows quick_records= table_records;
if (is_best_covering && !is_covering)
if (is_best_covering && !is_covering ||
is_covering && ref_key_quick_rows < select_limit)
continue;
if (table->quick_keys.is_set(nr))
quick_records= table->quick_rows[nr];