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MDEV-9522 Split sql_select.cc:can_change_cond_ref_to_const into virtual methods in Type_handler

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This commit is contained in:
Alexander Barkov 2017-01-13 17:25:16 +04:00
parent 306ce497a7
commit 59c58f6ec3
4 changed files with 151 additions and 69 deletions
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9
sql/item_cmpfunc.h
View file

@ -392,7 +392,7 @@ public:
Specifies which result type the function uses to compare its arguments.
This method is used in equal field propagation.
*/
virtual Item_result compare_type() const
virtual const Type_handler *compare_type_handler() const
{
/*
Have STRING_RESULT by default, which means the function compares
@ -400,7 +400,7 @@ public:
and for Item_func_spatial_rel.
Note, Item_bool_rowready_func2 overrides this default behaviour.
*/
return STRING_RESULT;
return &type_handler_varchar;
}
SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
{
@ -508,7 +508,10 @@ public:
return cmp.set_cmp_func(this, tmp_arg, tmp_arg + 1, true);
}
CHARSET_INFO *compare_collation() const { return cmp.compare_collation(); }
Item_result compare_type() const { return cmp.compare_type(); }
const Type_handler *compare_type_handler() const
{
return cmp.compare_type_handler();
}
Arg_comparator *get_comparator() { return &cmp; }
void cleanup()
{

72
sql/sql_select.cc
View file

@ -12927,7 +12927,7 @@ bool Item_func_eq::check_equality(THD *thd, COND_EQUAL *cond_equal,
}
return check_simple_equality(thd,
Context(ANY_SUBST,
compare_type(),
compare_type_handler()->cmp_type(),
compare_collation()),
left_item, right_item, cond_equal);
}
@ -13995,71 +13995,11 @@ can_change_cond_ref_to_const(Item_bool_func2 *target,
Item_bool_func2 *source,
Item *source_expr, Item *source_const)
{
if (!target_expr->eq(source_expr,0) ||
target_value == source_const ||
target->compare_type() != source->compare_type())
return false;
if (target->compare_type() == 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;
}
if (target->compare_type() == TIME_RESULT)
{
if (target_value->cmp_type() != TIME_RESULT)
{
/*
Can't rewrite:
WHERE COALESCE(time_column)='00:00:00'
AND COALESCE(time_column)=DATE'2015-09-11'
to
WHERE DATE'2015-09-11'='00:00:00'
AND COALESCE(time_column)=DATE'2015-09-11'
because the left part will erroneously try to parse '00:00:00'
as DATE, not as TIME.
TODO: It could still be rewritten to:
WHERE DATE'2015-09-11'=TIME'00:00:00'
AND COALESCE(time_column)=DATE'2015-09-11'
i.e. we need to replace both target_expr and target_value
at the same time. This is not supported yet.
*/
return false;
}
}
return true; // Non-string comparison
return target_expr->eq(source_expr,0) &&
target_value != source_const &&
target->compare_type_handler()->
can_change_cond_ref_to_const(target, target_expr, target_value,
source, source_expr, source_const);
}

93
sql/sql_type.cc
View file

@ -1057,6 +1057,99 @@ bool Type_handler_temporal_result::set_comparator_func(Arg_comparator *cmp) cons
}
/*************************************************************************/
bool Type_handler_temporal_result::
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)
const
{
if (source->compare_type_handler()->cmp_type() != TIME_RESULT)
return false;
/*
Can't rewrite:
WHERE COALESCE(time_column)='00:00:00'
AND COALESCE(time_column)=DATE'2015-09-11'
to
WHERE DATE'2015-09-11'='00:00:00'
AND COALESCE(time_column)=DATE'2015-09-11'
because the left part will erroneously try to parse '00:00:00'
as DATE, not as TIME.
TODO: It could still be rewritten to:
WHERE DATE'2015-09-11'=TIME'00:00:00'
AND COALESCE(time_column)=DATE'2015-09-11'
i.e. we need to replace both target_expr and target_value
at the same time. This is not supported yet.
*/
return target_value->cmp_type() == TIME_RESULT;
}
bool Type_handler_string_result::
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)
const
{
if (source->compare_type_handler()->cmp_type() != STRING_RESULT)
return false;
/*
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;
}
bool Type_handler_numeric::
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)
const
{
/*
The collations of "target" and "source" do not make sense for numeric
data types.
*/
return target->compare_type_handler() == source->compare_type_handler();
}
/*************************************************************************/
Item_cache *

46
sql/sql_type.h
View file

@ -32,6 +32,7 @@ class Item_func_hex;
class Item_hybrid_func;
class Item_func_min_max;
class Item_func_hybrid_field_type;
class Item_bool_func2;
class Item_func_between;
class Item_func_in;
class cmp_item;
@ -346,6 +347,31 @@ public:
virtual uint32 max_display_length(const Item *item) const= 0;
virtual int Item_save_in_field(Item *item, Field *field,
bool no_conversions) const= 0;
/**
Check if
WHERE expr=value AND expr=const
can be rewritten as:
WHERE const=value AND expr=const
"this" is the comparison handler that is used by "target".
@param target - the predicate expr=value,
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 predicate expr=const (or expr<=>const)
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".
*/
virtual 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) const= 0;
virtual Item_cache *Item_get_cache(THD *thd, const Item *item) const= 0;
virtual bool set_comparator_func(Arg_comparator *cmp) const= 0;
virtual bool Item_hybrid_func_fix_attributes(THD *thd, Item_hybrid_func *func,
@ -455,6 +481,14 @@ public:
DBUG_ASSERT(0);
return 1;
}
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) const
{
DBUG_ASSERT(0);
return false;
}
Item_cache *Item_get_cache(THD *thd, const Item *item) const;
bool set_comparator_func(Arg_comparator *cmp) const;
bool Item_hybrid_func_fix_attributes(THD *thd, Item_hybrid_func *func,
@ -558,6 +592,10 @@ public:
bool Item_func_min_max_get_date(Item_func_min_max*,
MYSQL_TIME *, ulonglong fuzzydate) const;
virtual ~Type_handler_numeric() { }
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) const;
};
@ -699,6 +737,10 @@ public:
const Type_std_attributes *item,
SORT_FIELD_ATTR *attr) const;
uint32 max_display_length(const Item *item) const;
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) const;
Item_cache *Item_get_cache(THD *thd, const Item *item) const;
bool set_comparator_func(Arg_comparator *cmp) const;
bool Item_sum_hybrid_fix_length_and_dec(Item_sum_hybrid *func) const;
@ -746,6 +788,10 @@ public:
SORT_FIELD_ATTR *attr) const;
uint32 max_display_length(const Item *item) const;
int Item_save_in_field(Item *item, Field *field, bool no_conversions) const;
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) const;
Item_cache *Item_get_cache(THD *thd, const Item *item) const;
bool set_comparator_func(Arg_comparator *cmp) const;
bool Item_hybrid_func_fix_attributes(THD *thd, Item_hybrid_func *func,