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MDEV-7152 Wrong result set for WHERE a='oe' COLLATE utf8_german2_ci AND a='oe'

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- The code that tested if
     WHERE expr=value AND expr=const
  can be rewritten to:
     WHERE const=value AND expr=const
  was incomplete in case of STRING_RESULT.
- Moving the test into a new function, to reduce duplicate code.
This commit is contained in:
Alexander Barkov
2015-01-18 01:54:11 +04:00
parent 09d54b37f5
commit c11a054a98
3 changed files with 116 additions and 16 deletions
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97
sql/sql_select.cc
View File

@ -12213,8 +12213,8 @@ public:
{ TRASH(ptr, size); }
Item *and_level;
Item_func *cmp_func;
COND_CMP(Item *a,Item_func *b) :and_level(a),cmp_func(b) {}
Item_bool_func2 *cmp_func;
COND_CMP(Item *a,Item_bool_func2 *b) :and_level(a),cmp_func(b) {}
};
/**
@ -13603,6 +13603,75 @@ static void update_const_equal_items(COND *cond, JOIN_TAB *tab, bool const_key)
}
/**
Check if
WHERE expr=value AND expr=const
can be rewritten as:
WHERE const=value AND expr=const
@param target - the target operator whose "expr" argument will be
replaced to "const".
@param target_expr - the target's "expr" which will be replaced to "const".
@param target_value - the target's second argument, it will remain unchanged.
@param source - the equality expression ("=" or "<=>") that
can be used to rewrite the "target" part
(under certain conditions, see the code).
@param source_expr - the source's "expr". It should be exactly equal to
the target's "expr" to make condition rewrite possible.
@param source_const - the source's "const" argument, it will be inserted
into "target" instead of "expr".
*/
static bool
can_change_cond_ref_to_const(Item_bool_func2 *target,
Item *target_expr, Item *target_value,
Item_bool_func2 *source,
Item *source_expr, Item *source_const)
{
if (!target_expr->eq(source_expr,0) ||
target_value == source_const ||
target_expr->cmp_context != source_expr->cmp_context)
return false;
if (target_expr->cmp_context == STRING_RESULT)
{
/*
In this example:
SET NAMES utf8 COLLATE utf8_german2_ci;
DROP TABLE IF EXISTS t1;
CREATE TABLE t1 (a CHAR(10) CHARACTER SET utf8);
INSERT INTO t1 VALUES ('o-umlaut'),('oe');
SELECT * FROM t1 WHERE a='oe' COLLATE utf8_german2_ci AND a='oe';
the query should return only the row with 'oe'.
It should not return 'o-umlaut', because 'o-umlaut' does not match
the right part of the condition: a='oe'
('o-umlaut' is not equal to 'oe' in utf8_general_ci,
which is the collation of the field "a").
If we change the right part from:
... AND a='oe'
to
... AND 'oe' COLLATE utf8_german2_ci='oe'
it will be evalulated to TRUE and removed from the condition,
so the overall query will be simplified to:
SELECT * FROM t1 WHERE a='oe' COLLATE utf8_german2_ci;
which will erroneously start to return both 'oe' and 'o-umlaut'.
So changing "expr" to "const" is not possible if the effective
collations of "target" and "source" are not exactly the same.
Note, the code before the fix for MDEV-7152 only checked that
collations of "source_const" and "target_value" are the same.
This was not enough, as the bug report demonstrated.
*/
return
target->compare_collation() == source->compare_collation() &&
target_value->collation.collation == source_const->collation.collation;
}
return true; // Non-string comparison
}
/*
change field = field to field = const for each found field = const in the
and_level
@ -13611,6 +13680,7 @@ static void update_const_equal_items(COND *cond, JOIN_TAB *tab, bool const_key)
static void
change_cond_ref_to_const(THD *thd, I_List<COND_CMP> *save_list,
Item *and_father, Item *cond,
Item_bool_func2 *field_value_owner,
Item *field, Item *value)
{
if (cond->type() == Item::COND_ITEM)
@ -13621,7 +13691,7 @@ change_cond_ref_to_const(THD *thd, I_List<COND_CMP> *save_list,
Item *item;
while ((item=li++))
change_cond_ref_to_const(thd, save_list,and_level ? cond : item, item,
field, value);
field_value_owner, field, value);
return;
}
if (cond->eq_cmp_result() == Item::COND_OK)
@ -13633,11 +13703,8 @@ change_cond_ref_to_const(THD *thd, I_List<COND_CMP> *save_list,
Item *right_item= args[1];
Item_func::Functype functype= func->functype();
if (right_item->eq(field,0) && left_item != value &&
right_item->cmp_context == field->cmp_context &&
(left_item->result_type() != STRING_RESULT ||
value->result_type() != STRING_RESULT ||
left_item->collation.collation == value->collation.collation))
if (can_change_cond_ref_to_const(func, right_item, left_item,
field_value_owner, field, value))
{
Item *tmp=value->clone_item();
if (tmp)
@ -13656,11 +13723,8 @@ change_cond_ref_to_const(THD *thd, I_List<COND_CMP> *save_list,
func->set_cmp_func();
}
}
else if (left_item->eq(field,0) && right_item != value &&
left_item->cmp_context == field->cmp_context &&
(right_item->result_type() != STRING_RESULT ||
value->result_type() != STRING_RESULT ||
right_item->collation.collation == value->collation.collation))
else if (can_change_cond_ref_to_const(func, left_item, right_item,
field_value_owner, field, value))
{
Item *tmp= value->clone_item();
if (tmp)
@ -13709,7 +13773,8 @@ propagate_cond_constants(THD *thd, I_List<COND_CMP> *save_list,
Item **args= cond_cmp->cmp_func->arguments();
if (!args[0]->const_item())
change_cond_ref_to_const(thd, &save,cond_cmp->and_level,
cond_cmp->and_level, args[0], args[1]);
cond_cmp->and_level,
cond_cmp->cmp_func, args[0], args[1]);
}
}
}
@ -13731,14 +13796,14 @@ propagate_cond_constants(THD *thd, I_List<COND_CMP> *save_list,
resolve_const_item(thd, &args[1], args[0]);
func->update_used_tables();
change_cond_ref_to_const(thd, save_list, and_father, and_father,
args[0], args[1]);
func, args[0], args[1]);
}
else if (left_const)
{
resolve_const_item(thd, &args[0], args[1]);
func->update_used_tables();
change_cond_ref_to_const(thd, save_list, and_father, and_father,
args[1], args[0]);
func, args[1], args[0]);
}
}
}