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Fix ORDER BY ... DESC optimization

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This commit is contained in:
monty@hundin.mysql.fi
2001-06-29 04:04:29 +03:00
parent 545e596ef7
commit f0dc189227
7 changed files with 377 additions and 106 deletions
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39
sql/sql_select.cc
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@@ -5153,9 +5153,11 @@ part_of_refkey(TABLE *table,Field *field)
** Returns: 1 if key is ok.
** 0 if key can't be used
** -1 if reverse key can be used
** used_key_parts is set to key parts used if length != 0
*****************************************************************************/
static int test_if_order_by_key(ORDER *order, TABLE *table, uint idx)
static int test_if_order_by_key(ORDER *order, TABLE *table, uint idx,
uint *used_key_parts)
{
KEY_PART_INFO *key_part,*key_part_end;
key_part=table->key_info[idx].key_part;
@@ -5187,6 +5189,7 @@ static int test_if_order_by_key(ORDER *order, TABLE *table, uint idx)
reverse=flag; // Remember if reverse
key_part++;
}
*used_key_parts= (uint) (key_part - table->key_info[idx].key_part);
return reverse;
}
@@ -5249,16 +5252,37 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
if (ref_key >= 0)
{
int order_direction;
uint used_key_parts;
/* Check if we get the rows in requested sorted order by using the key */
if ((usable_keys & ((key_map) 1 << ref_key)) &&
(order_direction = test_if_order_by_key(order,table,ref_key)))
(order_direction = test_if_order_by_key(order,table,ref_key,
&used_key_parts)))
{
if (order_direction == -1 && select && select->quick)
if (order_direction == -1)
{
// ORDER BY ref_key DESC
select->quick = new QUICK_SELECT_DESC(select->quick);
if (select->quick->error)
if (select && select->quick)
{
// ORDER BY ref_key DESC
QUICK_SELECT_DESC *tmp=new QUICK_SELECT_DESC(select->quick,
used_key_parts);
if (!tmp || tmp->error)
{
delete tmp;
DBUG_RETURN(0); // Reverse sort not supported
}
select->quick=tmp;
DBUG_RETURN(1);
}
if (tab->ref.key_parts < used_key_parts)
{
/*
SELECT * FROM t1 WHERE a=1 ORDER BY a DESC,b DESC
TODO:
Add a new traversal function to read last matching row and
traverse backwards.
*/
DBUG_RETURN(0);
}
}
DBUG_RETURN(1); /* No need to sort */
}
@@ -5280,10 +5304,11 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
for (nr=0; keys ; keys>>=1, nr++)
{
uint not_used;
if (keys & 1)
{
int flag;
if ((flag=test_if_order_by_key(order,table,nr)))
if ((flag=test_if_order_by_key(order, table, nr, &not_used)))
{
if (!no_changes)
{