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Bug #31001: ORDER BY DESC in InnoDB not working

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The optimizer sets index traversal in reverse order only if there are 
 used key parts that are not compared to a constant.
However using the primary key as an ORDER BY suffix rendered the check
incomplete : going in reverse order must still be used even if 
all the parts of the secondary key are compared to a constant.

Fixed by relaxing the check and set reverse traversal even when all
the secondary index keyparts are compared to a const.
Also account for the case when all the primary keys are compared to a
constant.
This commit is contained in:
gkodinov/kgeorge@magare.gmz
2007-09-14 17:43:14 +03:00
parent 2e7306d503
commit a2afc56f61
3 changed files with 127 additions and 1 deletions
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8
sql/sql_select.cc
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@ -12063,6 +12063,12 @@ static int test_if_order_by_key(ORDER *order, TABLE *table, uint idx,
for (; const_key_parts & 1 ; const_key_parts>>= 1)
key_part++;
/*
The primary and secondary key parts were all const (i.e. there's
one row). The sorting doesn't matter.
*/
if (key_part == key_part_end && reverse == 0)
DBUG_RETURN(1);
}
else
DBUG_RETURN(0);
@ -12480,7 +12486,7 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
}
DBUG_RETURN(1);
}
if (tab->ref.key_parts < used_key_parts)
if (tab->ref.key_parts <= used_key_parts)
{
/*
SELECT * FROM t1 WHERE a=1 ORDER BY a DESC,b DESC