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Fix for BUG#16710.

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The bug was due to a missed case in the detection of whether an index
can be used for loose scan. More precisely, the range optimizer chose
to use loose index scan for queries for which the condition(s) over
an index key part could not be pushed to the index together with the
loose scan.

As a result, loose index scan was selecting the first row in the
index with a given GROUP BY prefix, and was applying the WHERE
clause after that, while it should have inspected all rows with
the given prefix, and apply the WHERE clause to all of them.

The fix detects and skips such cases.
This commit is contained in:
timour@mysql.com
2006-03-31 12:34:28 +03:00
parent 86332f4369
commit eed7cf09dd
5 changed files with 78 additions and 1 deletions
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26
sql/opt_range.cc
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@@ -6876,6 +6876,7 @@ cost_group_min_max(TABLE* table, KEY *index_info, uint used_key_parts,
bool have_min, bool have_max,
double *read_cost, ha_rows *records);
/*
Test if this access method is applicable to a GROUP query with MIN/MAX
functions, and if so, construct a new TRP object.
@@ -7282,11 +7283,36 @@ get_best_group_min_max(PARAM *param, SEL_TREE *tree)
}
else if (min_max_arg_part &&
(min_max_arg_part - first_non_group_part > 0))
{
/*
There is a gap but no range tree, thus no predicates at all for the
non-group keyparts.
*/
goto next_index;
}
else if (first_non_group_part && join->conds)
{
/*
If there is no MIN/MAX function in the query, but some index
key part is referenced in the WHERE clause, then this index
cannot be used because the WHERE condition over the keypart's
field cannot be 'pushed' to the index (because there is no
range 'tree'), and the WHERE clause must be evaluated before
GROUP BY/DISTINCT.
*/
/*
Store the first and last keyparts that need to be analyzed
into one array that can be passed as parameter.
*/
KEY_PART_INFO *key_part_range[2];
key_part_range[0]= first_non_group_part;
key_part_range[1]= last_part;
/* Check if cur_part is referenced in the WHERE clause. */
if (join->conds->walk(&Item::find_item_in_field_list_processor,
(byte*) key_part_range))
goto next_index;
}
}
/*