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Fix for bug#52051: Aggregate functions incorrectly returns

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NULL from outer join query
      
      Problem: optimising MIN/MAX() queries without GROUP BY clause
      by replacing the aggregate expression with a constant, we may set it
      to NULL disregarding the fact that there may be outer joins involved.
      
      Fix: don't replace MIN/MAX() with NULL if there're outer joins.
      
      Note: the fix itself is just
      - if (!count)
      + if (!count && !outer_tables)
          set to NULL
      
      The rest of the patch eliminates repeated code to improve speed
      and for easy maintenance of the code.


mysql-test/r/group_by.result:
          Fix for bug#52051: Aggregate functions incorrectly returns
          NULL from outer join query
            - test result.
mysql-test/t/group_by.test:
          Fix for bug#52051: Aggregate functions incorrectly returns
          NULL from outer join query
            - test case.
sql/opt_sum.cc:
          Fix for bug#52051: Aggregate functions incorrectly returns
          NULL from outer join query
            - optimising MIN/MAX() queries without GROUP BY clause by
          replacing them with a constant, take into account that
          there're may be outer joins involved.
            - repeated code for MIN/MAX optimization in the opt_sum_query()
          eliminated by introducing new functions that read MIN/MAX values
          using index and combining MIN/MAX cases to one.
This commit is contained in:
Ramil Kalimullin 2010-05-12 20:10:33 +04:00
parent 330864fcda
commit feb03a82f2
3 changed files with 170 additions and 161 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

20
mysql-test/r/group_by.result
View file

@ -1790,4 +1790,24 @@ aa b COUNT( b)
1 10 1
DROP TABLE t1, t2;
#
# Bug#52051: Aggregate functions incorrectly returns NULL from outer
# join query
#
CREATE TABLE t1 (a INT PRIMARY KEY);
CREATE TABLE t2 (a INT PRIMARY KEY);
INSERT INTO t2 VALUES (1), (2);
EXPLAIN SELECT MIN(t2.a) FROM t2 LEFT JOIN t1 ON t2.a = t1.a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
SELECT MIN(t2.a) FROM t2 LEFT JOIN t1 ON t2.a = t1.a;
MIN(t2.a)
1
EXPLAIN SELECT MAX(t2.a) FROM t2 LEFT JOIN t1 ON t2.a = t1.a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
SELECT MAX(t2.a) FROM t2 LEFT JOIN t1 ON t2.a = t1.a;
MAX(t2.a)
2
DROP TABLE t1, t2;
#
# End of 5.1 tests

15
mysql-test/t/group_by.test
View file

@ -1205,6 +1205,21 @@ SELECT (SELECT t2.a FROM t2 WHERE t2.a = t1.a) aa, b, COUNT( b)
DROP TABLE t1, t2;
--echo #
--echo # Bug#52051: Aggregate functions incorrectly returns NULL from outer
--echo # join query
--echo #
CREATE TABLE t1 (a INT PRIMARY KEY);
CREATE TABLE t2 (a INT PRIMARY KEY);
INSERT INTO t2 VALUES (1), (2);
EXPLAIN SELECT MIN(t2.a) FROM t2 LEFT JOIN t1 ON t2.a = t1.a;
SELECT MIN(t2.a) FROM t2 LEFT JOIN t1 ON t2.a = t1.a;
EXPLAIN SELECT MAX(t2.a) FROM t2 LEFT JOIN t1 ON t2.a = t1.a;
SELECT MAX(t2.a) FROM t2 LEFT JOIN t1 ON t2.a = t1.a;
DROP TABLE t1, t2;
--echo #
--echo # End of 5.1 tests

296
sql/opt_sum.cc
View file

@ -88,6 +88,123 @@ static ulonglong get_exact_record_count(TABLE_LIST *tables)
}
/**
Use index to read MIN(field) value.
@param table Table object
@param ref Reference to the structure where we store the key value
@item_field Field used in MIN()
@range_fl Whether range endpoint is strict less than
@prefix_len Length of common key part for the range
@retval
0 No errors
HA_ERR_... Otherwise
*/
static int get_index_min_value(TABLE *table, TABLE_REF *ref,
Item_field *item_field, uint range_fl,
uint prefix_len)
{
int error;
if (!ref->key_length)
error= table->file->index_first(table->record[0]);
else
{
/*
Use index to replace MIN/MAX functions with their values
according to the following rules:
1) Insert the minimum non-null values where the WHERE clause still
matches, or
2) a NULL value if there are only NULL values for key_part_k.
3) Fail, producing a row of nulls
Implementation: Read the smallest value using the search key. If
the interval is open, read the next value after the search
key. If read fails, and we're looking for a MIN() value for a
nullable column, test if there is an exact match for the key.
*/
if (!(range_fl & NEAR_MIN))
/*
Closed interval: Either The MIN argument is non-nullable, or
we have a >= predicate for the MIN argument.
*/
error= table->file->index_read_map(table->record[0],
ref->key_buff,
make_prev_keypart_map(ref->key_parts),
HA_READ_KEY_OR_NEXT);
else
{
/*
Open interval: There are two cases:
1) We have only MIN() and the argument column is nullable, or
2) there is a > predicate on it, nullability is irrelevant.
We need to scan the next bigger record first.
*/
error= table->file->index_read_map(table->record[0],
ref->key_buff,
make_prev_keypart_map(ref->key_parts),
HA_READ_AFTER_KEY);
/*
If the found record is outside the group formed by the search
prefix, or there is no such record at all, check if all
records in that group have NULL in the MIN argument
column. If that is the case return that NULL.
Check if case 1 from above holds. If it does, we should read
the skipped tuple.
*/
if (item_field->field->real_maybe_null() &&
ref->key_buff[prefix_len] == 1 &&
/*
Last keypart (i.e. the argument to MIN) is set to NULL by
find_key_for_maxmin only if all other keyparts are bound
to constants in a conjunction of equalities. Hence, we
can detect this by checking only if the last keypart is
NULL.
*/
(error == HA_ERR_KEY_NOT_FOUND ||
key_cmp_if_same(table, ref->key_buff, ref->key, prefix_len)))
{
DBUG_ASSERT(item_field->field->real_maybe_null());
error= table->file->index_read_map(table->record[0],
ref->key_buff,
make_prev_keypart_map(ref->key_parts),
HA_READ_KEY_EXACT);
}
}
}
return error;
}
/**
Use index to read MAX(field) value.
@param table Table object
@param ref Reference to the structure where we store the key value
@range_fl Whether range endpoint is strict greater than
@retval
0 No errors
HA_ERR_... Otherwise
*/
static int get_index_max_value(TABLE *table, TABLE_REF *ref, uint range_fl)
{
return (ref->key_length ?
table->file->index_read_map(table->record[0], ref->key_buff,
make_prev_keypart_map(ref->key_parts),
range_fl & NEAR_MAX ?
HA_READ_BEFORE_KEY :
HA_READ_PREFIX_LAST_OR_PREV) :
table->file->index_last(table->record[0]));
}
/**
Substitutes constants for some COUNT(), MIN() and MAX() functions.
@ -220,9 +337,11 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
const_result= 0;
break;
case Item_sum::MIN_FUNC:
case Item_sum::MAX_FUNC:
{
int is_max= test(item_sum->sum_func() == Item_sum::MAX_FUNC);
/*
If MIN(expr) is the first part of a key or if all previous
If MIN/MAX(expr) is the first part of a key or if all previous
parts of the key is found in the COND, then we can use
indexes to find the key.
*/
@ -241,89 +360,26 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
Look for a partial key that can be used for optimization.
If we succeed, ref.key_length will contain the length of
this key, while prefix_len will contain the length of
the beginning of this key without field used in MIN().
the beginning of this key without field used in MIN/MAX().
Type of range for the key part for this field will be
returned in range_fl.
*/
if (table->file->inited || (outer_tables & table->map) ||
!find_key_for_maxmin(0, &ref, item_field->field, conds,
!find_key_for_maxmin(is_max, &ref, item_field->field, conds,
&range_fl, &prefix_len))
{
const_result= 0;
break;
}
error= table->file->ha_index_init((uint) ref.key, 1);
table->file->ha_index_init((uint) ref.key, 1);
if (!ref.key_length)
error= table->file->index_first(table->record[0]);
else
{
/*
Use index to replace MIN/MAX functions with their values
according to the following rules:
1) Insert the minimum non-null values where the WHERE clause still
matches, or
2) a NULL value if there are only NULL values for key_part_k.
3) Fail, producing a row of nulls
error= is_max ?
get_index_max_value(table, &ref, range_fl) :
get_index_min_value(table, &ref, item_field, range_fl,
prefix_len);
Implementation: Read the smallest value using the search key. If
the interval is open, read the next value after the search
key. If read fails, and we're looking for a MIN() value for a
nullable column, test if there is an exact match for the key.
*/
if (!(range_fl & NEAR_MIN))
/*
Closed interval: Either The MIN argument is non-nullable, or
we have a >= predicate for the MIN argument.
*/
error= table->file->index_read_map(table->record[0],
ref.key_buff,
make_prev_keypart_map(ref.key_parts),
HA_READ_KEY_OR_NEXT);
else
{
/*
Open interval: There are two cases:
1) We have only MIN() and the argument column is nullable, or
2) there is a > predicate on it, nullability is irrelevant.
We need to scan the next bigger record first.
*/
error= table->file->index_read_map(table->record[0],
ref.key_buff,
make_prev_keypart_map(ref.key_parts),
HA_READ_AFTER_KEY);
/*
If the found record is outside the group formed by the search
prefix, or there is no such record at all, check if all
records in that group have NULL in the MIN argument
column. If that is the case return that NULL.
Check if case 1 from above holds. If it does, we should read
the skipped tuple.
*/
if (item_field->field->real_maybe_null() &&
ref.key_buff[prefix_len] == 1 &&
/*
Last keypart (i.e. the argument to MIN) is set to NULL by
find_key_for_maxmin only if all other keyparts are bound
to constants in a conjunction of equalities. Hence, we
can detect this by checking only if the last keypart is
NULL.
*/
(error == HA_ERR_KEY_NOT_FOUND ||
key_cmp_if_same(table, ref.key_buff, ref.key, prefix_len)))
{
DBUG_ASSERT(item_field->field->real_maybe_null());
error= table->file->index_read_map(table->record[0],
ref.key_buff,
make_prev_keypart_map(ref.key_parts),
HA_READ_KEY_EXACT);
}
}
}
/* Verify that the read tuple indeed matches the search key */
if (!error && reckey_in_range(0, &ref, item_field->field,
if (!error && reckey_in_range(is_max, &ref, item_field->field,
conds, range_fl, prefix_len))
error= HA_ERR_KEY_NOT_FOUND;
table->set_keyread(FALSE);
@ -352,98 +408,16 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
const_result= 0;
break;
}
if (!count)
{
/* If count == 0, then we know that is_exact_count == TRUE. */
((Item_sum_min*) item_sum)->clear(); /* Set to NULL. */
}
else
((Item_sum_min*) item_sum)->reset(); /* Set to the constant value. */
((Item_sum_min*) item_sum)->make_const();
recalc_const_item= 1;
break;
}
case Item_sum::MAX_FUNC:
{
/*
If MAX(expr) is the first part of a key or if all previous
parts of the key is found in the COND, then we can use
indexes to find the key.
If count == 0 (so is_exact_count == TRUE) and
there're no outer joins, set to NULL,
otherwise set to the constant value.
*/
Item *expr=item_sum->get_arg(0);
if (expr->real_item()->type() == Item::FIELD_ITEM)
{
uchar key_buff[MAX_KEY_LENGTH];
TABLE_REF ref;
uint range_fl, prefix_len;
ref.key_buff= key_buff;
Item_field *item_field= (Item_field*) (expr->real_item());
TABLE *table= item_field->field->table;
/*
Look for a partial key that can be used for optimization.
If we succeed, ref.key_length will contain the length of
this key, while prefix_len will contain the length of
the beginning of this key without field used in MAX().
Type of range for the key part for this field will be
returned in range_fl.
*/
if (table->file->inited || (outer_tables & table->map) ||
!find_key_for_maxmin(1, &ref, item_field->field, conds,
&range_fl, &prefix_len))
{
const_result= 0;
break;
}
error= table->file->ha_index_init((uint) ref.key, 1);
if (!ref.key_length)
error= table->file->index_last(table->record[0]);
else
error= table->file->index_read_map(table->record[0], key_buff,
make_prev_keypart_map(ref.key_parts),
range_fl & NEAR_MAX ?
HA_READ_BEFORE_KEY :
HA_READ_PREFIX_LAST_OR_PREV);
if (!error && reckey_in_range(1, &ref, item_field->field,
conds, range_fl, prefix_len))
error= HA_ERR_KEY_NOT_FOUND;
table->set_keyread(FALSE);
table->file->ha_index_end();
if (error)
{
if (error == HA_ERR_KEY_NOT_FOUND || error == HA_ERR_END_OF_FILE)
return HA_ERR_KEY_NOT_FOUND; // No rows matching WHERE
/* HA_ERR_LOCK_DEADLOCK or some other error */
table->file->print_error(error, MYF(0));
table->in_use->fatal_error();
return(error);
}
removed_tables|= table->map;
}
else if (!expr->const_item() || !is_exact_count)
{
/*
The optimization is not applicable in both cases:
(a) 'expr' is a non-constant expression. Then we can't
replace 'expr' by a constant.
(b) 'expr' is a costant. According to ANSI, MIN/MAX must return
NULL if the query does not return any rows. Thus, if we are not
able to determine if the query returns any rows, we can't apply
the optimization and replace MIN/MAX with a constant.
*/
const_result= 0;
break;
}
if (!count)
{
/* If count != 1, then we know that is_exact_count == TRUE. */
((Item_sum_max*) item_sum)->clear(); /* Set to NULL. */
}
if (!count && !outer_tables)
item_sum->clear();
else
((Item_sum_max*) item_sum)->reset(); /* Set to the constant value. */
((Item_sum_max*) item_sum)->make_const();
item_sum->reset();
item_sum->make_const();
recalc_const_item= 1;
break;
}