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MDEV-9181 (NULLIF(count(table.col)), 0) gives wrong result on 10.1.x
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Wrapping args[0] and args[2] into an Item_cache for aggregate functions.
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Alexander Barkov committed Jan 28, 2016
1 parent 5092ab2 commit ce40cca
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60 changes: 60 additions & 0 deletions mysql-test/r/null.result
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Original file line number Diff line number Diff line change
Expand Up @@ -1465,5 +1465,65 @@ Warnings:
Note 1003 select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((`test`.`t1`.`a` = 2020) and ((case when 2020 = 2010 then NULL else `test`.`t1`.`a` end) = concat('2020',rand())))
DROP TABLE t1;
#
# MDEV-9181 (NULLIF(count(table.col)), 0) gives wrong result on 10.1.x
#
CREATE TABLE t1 (c1 varchar(50) DEFAULT NULL);
INSERT INTO t1 (c1) VALUES ('hello'), ('hello\r\n'), ('hello'),('hello');
SELECT NULLIF(COUNT(c1),0) FROM t1;
NULLIF(COUNT(c1),0)
4
SELECT CASE WHEN COUNT(c1)=0 THEN NULL ELSE COUNT(c1) END FROM t1;
CASE WHEN COUNT(c1)=0 THEN NULL ELSE COUNT(c1) END
4
SELECT NULLIF(COUNT(c1)+0,0) AS c1,NULLIF(CAST(COUNT(c1) AS SIGNED),0) AS c2,NULLIF(CONCAT(COUNT(c1)),0) AS c3 FROM t1;
c1 c2 c3
4 4 4
SELECT NULLIF(COUNT(DISTINCT c1),0) FROM t1;
NULLIF(COUNT(DISTINCT c1),0)
2
SELECT CASE WHEN COUNT(DISTINCT c1)=0 THEN NULL ELSE COUNT(DISTINCT c1) END FROM t1;
CASE WHEN COUNT(DISTINCT c1)=0 THEN NULL ELSE COUNT(DISTINCT c1) END
2
DROP TABLE t1;
CREATE TABLE t1 (
id INT NOT NULL,
c1 INT DEFAULT NULL
);
INSERT INTO t1 VALUES (1,1),(1,2),(2,3),(2,4);
SELECT NULLIF(COUNT(c1),0) AS c1,NULLIF(COUNT(c1)+0,0) AS c1_wrapped,CASE WHEN COUNT(c1) IS NULL THEN 0 ELSE COUNT(c1) END AS c1_case FROM t1 GROUP BY id;
c1 c1_wrapped c1_case
2 2 2
2 2 2
DROP TABLE t1;
CREATE TABLE t1 (a INT);
INSERT INTO t1 VALUES (1),(2),(3);
SET @a=0;
SELECT NULLIF(LAST_VALUE(@a:=@a+1,a),0) FROM t1;
NULLIF(LAST_VALUE(@a:=@a+1,a),0)
1
2
3
SELECT @a;
@a
6
SET @a=0;
SELECT NULLIF(AVG(a),0), NULLIF(AVG(LAST_VALUE(@a:=@a+1,a)),0) FROM t1;
NULLIF(AVG(a),0) NULLIF(AVG(LAST_VALUE(@a:=@a+1,a)),0)
2.0000 2.0000
SELECT @a;
@a
3
EXPLAIN EXTENDED SELECT NULLIF(a,0) FROM t1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3 100.00
Warnings:
Note 1003 select nullif(`test`.`t1`.`a`,0) AS `NULLIF(a,0)` from `test`.`t1`
EXPLAIN EXTENDED SELECT NULLIF(AVG(a),0) FROM t1;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3 100.00
Warnings:
Note 1003 select nullif(<cache>(avg(`test`.`t1`.`a`)),0) AS `NULLIF(AVG(a),0)` from `test`.`t1`
DROP TABLE t1;
#
# End of 10.1 tests
#
39 changes: 39 additions & 0 deletions mysql-test/t/null.test
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Original file line number Diff line number Diff line change
Expand Up @@ -909,6 +909,45 @@ EXPLAIN EXTENDED
SELECT * FROM t1 WHERE a=2020 AND NULLIF(a,2010)=CONCAT('2020',RAND());
DROP TABLE t1;

--echo #
--echo # MDEV-9181 (NULLIF(count(table.col)), 0) gives wrong result on 10.1.x
--echo #
CREATE TABLE t1 (c1 varchar(50) DEFAULT NULL);
INSERT INTO t1 (c1) VALUES ('hello'), ('hello\r\n'), ('hello'),('hello');
SELECT NULLIF(COUNT(c1),0) FROM t1;
SELECT CASE WHEN COUNT(c1)=0 THEN NULL ELSE COUNT(c1) END FROM t1;
SELECT NULLIF(COUNT(c1)+0,0) AS c1,NULLIF(CAST(COUNT(c1) AS SIGNED),0) AS c2,NULLIF(CONCAT(COUNT(c1)),0) AS c3 FROM t1;
SELECT NULLIF(COUNT(DISTINCT c1),0) FROM t1;
SELECT CASE WHEN COUNT(DISTINCT c1)=0 THEN NULL ELSE COUNT(DISTINCT c1) END FROM t1;
DROP TABLE t1;

CREATE TABLE t1 (
id INT NOT NULL,
c1 INT DEFAULT NULL
);
INSERT INTO t1 VALUES (1,1),(1,2),(2,3),(2,4);
SELECT NULLIF(COUNT(c1),0) AS c1,NULLIF(COUNT(c1)+0,0) AS c1_wrapped,CASE WHEN COUNT(c1) IS NULL THEN 0 ELSE COUNT(c1) END AS c1_case FROM t1 GROUP BY id;
DROP TABLE t1;

# Testing with side effects

CREATE TABLE t1 (a INT);
INSERT INTO t1 VALUES (1),(2),(3);
SET @a=0;
SELECT NULLIF(LAST_VALUE(@a:=@a+1,a),0) FROM t1;
SELECT @a;
SET @a=0;
SELECT NULLIF(AVG(a),0), NULLIF(AVG(LAST_VALUE(@a:=@a+1,a)),0) FROM t1;
SELECT @a;

# There should not be cache in here:

EXPLAIN EXTENDED SELECT NULLIF(a,0) FROM t1;

# But there should be a cache in here:
EXPLAIN EXTENDED SELECT NULLIF(AVG(a),0) FROM t1;

DROP TABLE t1;

--echo #
--echo # End of 10.1 tests
Expand Down
45 changes: 37 additions & 8 deletions sql/item.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3629,6 +3629,11 @@ class Used_tables_and_const_cache
used_tables_cache|= item->used_tables();
const_item_cache&= item->const_item();
}
void used_tables_and_const_cache_update_and_join(Item *item)
{
item->update_used_tables();
used_tables_and_const_cache_join(item);
}
/*
Call update_used_tables() for all "argc" items in the array "argv"
and join with the current cache.
Expand All @@ -3638,10 +3643,7 @@ class Used_tables_and_const_cache
void used_tables_and_const_cache_update_and_join(uint argc, Item **argv)
{
for (uint i=0 ; i < argc ; i++)
{
argv[i]->update_used_tables();
used_tables_and_const_cache_join(argv[i]);
}
used_tables_and_const_cache_update_and_join(argv[i]);
}
/*
Call update_used_tables() for all items in the list
Expand All @@ -3654,10 +3656,7 @@ class Used_tables_and_const_cache
List_iterator_fast<Item> li(list);
Item *item;
while ((item=li++))
{
item->update_used_tables();
used_tables_and_const_cache_join(item);
}
used_tables_and_const_cache_update_and_join(item);
}
};

Expand Down Expand Up @@ -5073,6 +5072,12 @@ class Item_cache: public Item_basic_constant
return (this->*processor)(arg);
}
virtual Item *safe_charset_converter(THD *thd, CHARSET_INFO *tocs);
void split_sum_func2_example(THD *thd, Item **ref_pointer_array,
List<Item> &fields, uint flags)
{
example->split_sum_func2(thd, ref_pointer_array, fields, &example, flags);
}
Item *get_example() const { return example; }
};


Expand Down Expand Up @@ -5177,6 +5182,30 @@ class Item_cache_str: public Item_cache
bool cache_value();
};


class Item_cache_str_for_nullif: public Item_cache_str
{
public:
Item_cache_str_for_nullif(THD *thd, const Item *item)
:Item_cache_str(thd, item)
{ }
Item *safe_charset_converter(THD *thd, CHARSET_INFO *tocs)
{
/**
Item_cache_str::safe_charset_converter() returns a new Item_cache
with Item_func_conv_charset installed on "example". The original
Item_cache is not referenced (neither directly nor recursively)
from the result of Item_cache_str::safe_charset_converter().
For NULLIF() purposes we need a different behavior:
we need a new instance of Item_func_conv_charset,
with the original Item_cache referenced in args[0]. See MDEV-9181.
*/
return Item::safe_charset_converter(thd, tocs);
}
};


class Item_cache_row: public Item_cache
{
Item_cache **values;
Expand Down
144 changes: 138 additions & 6 deletions sql/item_cmpfunc.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -2531,12 +2531,137 @@ bool Item_func_if::date_op(MYSQL_TIME *ltime, uint fuzzydate)
}


void Item_func_nullif::split_sum_func(THD *thd, Item **ref_pointer_array,
List<Item> &fields, uint flags)
{
if (m_cache)
{
flags|= SPLIT_SUM_SKIP_REGISTERED; // See Item_func::split_sum_func
m_cache->split_sum_func2_example(thd, ref_pointer_array, fields, flags);
args[1]->split_sum_func2(thd, ref_pointer_array, fields, &args[1], flags);
}
else
{
Item_func::split_sum_func(thd, ref_pointer_array, fields, flags);
}
}


void Item_func_nullif::update_used_tables()
{
if (m_cache)
{
used_tables_and_const_cache_init();
used_tables_and_const_cache_update_and_join(m_cache->get_example());
used_tables_and_const_cache_update_and_join(arg_count, args);
}
else
{
Item_func::update_used_tables();
}
}



void
Item_func_nullif::fix_length_and_dec()
{
if (!args[2]) // Only false if EOM
return;

DBUG_ASSERT(args[0] == args[2]);
THD *thd= current_thd;
if (args[0]->type() == SUM_FUNC_ITEM)
{
/*
NULLIF(l_expr, r_expr)
is calculated in the way to return a result equal to:
CASE WHEN l_expr = r_expr THEN NULL ELSE r_expr END.
There's nothing special with r_expr, because it's referenced
only by args[1] and nothing else.
l_expr needs a special treatment, as it's referenced by both
args[0] and args[2] initially.
args[0] and args[2] can be replaced:
- to Item_func_conv_charset by character set aggregation routines
- to a constant Item by equal field propagation routines
(in case of Item_field)
For aggregate functions we have to wrap the original args[0]/args[2]
into Item_cache (see MDEV-9181). In this case the Item_cache
instance becomes the subject to character set conversion instead of
the original args[0]/args[2], while the original args[0]/args[2] get
hidden inside the cache.
Some examples of what NULLIF can end up with after argument
substitution (we don't mention args[1] here for simplicity):
1. l_expr is not an aggragate function:
a. No conversion happened.
args[0] and args[2] were not replaced to something else
(i.e. neither by character set conversion, nor by propagation):
args[0] \
l_expr
args[2] /
b. Conversion of args[0] happened.
args[0] was replaced, e.g. to Item_func_conv_charset:
args[0] > Item_func_conv_charset \
l_expr
args[2] >------------------------/
c. Conversion of args[2] happened:
args[0] >------------------------\
l_expr
args[2] > Item_func_conv_charset /
d. Conversion of both args[0] and args[2] happened
(e.g. by equal field propagation).
args[0] > Item_int
args[2] > Item_int
2. In case if l_expr is an aggregate function:
a. No conversion happened:
args[0] \
Item_cache > l_expr
args[2] /
b. Conversion of args[0] happened:
args[0] > Item_func_conv_charset \
Item_cache > l_expr
args[2] >------------------------/
c. Conversion of args[2] happened:
args[0] >------------------------\
Item_cache > l_expr
args[2] > Item_func_conv_charset /
d. Conversion of both args[0] and args[2] happened.
(e.g. by equal expression propagation)
TODO: check if it's possible (and add an example query if so).
*/
m_cache= args[0]->cmp_type() == STRING_RESULT ?
new (thd->mem_root) Item_cache_str_for_nullif(thd, args[0]) :
Item_cache::get_cache(thd, args[0]);
m_cache->setup(current_thd, args[0]);
m_cache->store(args[0]);
m_cache->set_used_tables(args[0]->used_tables());
args[0]= args[2]= m_cache;
}
set_handler_by_field_type(args[2]->field_type());
collation.set(args[2]->collation);
decimals= args[2]->decimals;
Expand Down Expand Up @@ -2611,6 +2736,13 @@ void Item_func_nullif::print(String *str, enum_query_type query_type)
}


int Item_func_nullif::compare()
{
if (m_cache)
m_cache->cache_value();
return cmp.compare();
}

/**
@note
Note that we have to evaluate the first argument twice as the compare
Expand All @@ -2626,7 +2758,7 @@ Item_func_nullif::real_op()
{
DBUG_ASSERT(fixed == 1);
double value;
if (!cmp.compare())
if (!compare())
{
null_value=1;
return 0.0;
Expand All @@ -2641,7 +2773,7 @@ Item_func_nullif::int_op()
{
DBUG_ASSERT(fixed == 1);
longlong value;
if (!cmp.compare())
if (!compare())
{
null_value=1;
return 0;
Expand All @@ -2656,7 +2788,7 @@ Item_func_nullif::str_op(String *str)
{
DBUG_ASSERT(fixed == 1);
String *res;
if (!cmp.compare())
if (!compare())
{
null_value=1;
return 0;
Expand All @@ -2672,7 +2804,7 @@ Item_func_nullif::decimal_op(my_decimal * decimal_value)
{
DBUG_ASSERT(fixed == 1);
my_decimal *res;
if (!cmp.compare())
if (!compare())
{
null_value=1;
return 0;
Expand All @@ -2687,7 +2819,7 @@ bool
Item_func_nullif::date_op(MYSQL_TIME *ltime, uint fuzzydate)
{
DBUG_ASSERT(fixed == 1);
if (!cmp.compare())
if (!compare())
return (null_value= true);
return (null_value= args[2]->get_date(ltime, fuzzydate));
}
Expand All @@ -2696,7 +2828,7 @@ Item_func_nullif::date_op(MYSQL_TIME *ltime, uint fuzzydate)
bool
Item_func_nullif::is_null()
{
return (null_value= (!cmp.compare() ? 1 : args[2]->null_value));
return (null_value= (!compare() ? 1 : args[2]->null_value));
}


Expand Down
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