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BUG#24127: (a,b) IN (SELECT c,d ...) can produce wrong results if a and/or b are NULLs:

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- Make the code produce correct result: use an array of triggers to turn on/off equalities for each
  compared column. Also turn on/off optimizations based on those equalities.
- Make EXPLAIN output show "Full scan on NULL key" for tables for which we switch between
  ref/unique_subquery/index_subquery and ALL access.
- index_subquery engine now has HAVING clause when it is needed, and it is
  displayed in EXPLAIN EXTENDED
- Fix incorrect presense of "Using index" for index/unique-based subqueries (BUG#22930)
// bk trigger note: this commit refers to BUG#24127
This commit is contained in:
sergefp@mysql.com
2007-01-12 23:22:41 +03:00
parent 5236794855
commit c3f46e1f26
14 changed files with 1129 additions and 247 deletions
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190
sql/sql_select.cc
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@ -513,72 +513,88 @@ err:
/*
test if it is known for optimisation IN subquery
Remove the predicates pushed down into the subquery
SYNOPSIS
JOIN::test_in_subselect()
where - pointer for variable in which conditions should be
stored if subquery is known
JOIN::remove_subq_pushed_predicates()
where IN Must be NULL
OUT The remaining WHERE condition, or NULL
RETURN
1 - known
0 - unknown
DESCRIPTION
Given that this join will be executed using (unique|index)_subquery,
without "checking NULL", remove the predicates that were pushed down
into the subquery.
We can remove the equalities that will be guaranteed to be true by the
fact that subquery engine will be using index lookup.
If the subquery compares scalar values, we can remove the condition that
was wrapped into trig_cond (it will be checked when needed by the subquery
engine)
If the subquery compares row values, we need to keep the wrapped
equalities in the WHERE clause: when the left (outer) tuple has both NULL
and non-NULL values, we'll do a full table scan and will rely on the
equalities corresponding to non-NULL parts of left tuple to filter out
non-matching records.
*/
bool JOIN::test_in_subselect(Item **where)
void JOIN::remove_subq_pushed_predicates(Item **where)
{
if (conds->type() == Item::FUNC_ITEM &&
((Item_func *)this->conds)->functype() == Item_func::EQ_FUNC &&
((Item_func *)conds)->arguments()[0]->type() == Item::REF_ITEM &&
((Item_func *)conds)->arguments()[1]->type() == Item::FIELD_ITEM)
{
join_tab->info= "Using index";
*where= 0;
return 1;
return;
}
if (conds->type() == Item::COND_ITEM &&
((class Item_func *)this->conds)->functype() ==
Item_func::COND_AND_FUNC)
{
if ((*where= remove_additional_cond(conds)))
join_tab->info= "Using index; Using where";
else
join_tab->info= "Using index";
return 1;
*where= remove_additional_cond(conds);
}
return 0;
}
/*
Check if the passed HAVING clause is a clause added by subquery optimizer
Index lookup-based subquery: save some flags for EXPLAIN output
SYNOPSIS
is_having_subq_predicates()
having Having clause
save_index_subquery_explain_info()
join_tab Subquery's join tab (there is only one as index lookup is
only used for subqueries that are single-table SELECTs)
where Subquery's WHERE clause
RETURN
TRUE The passed HAVING clause was added by the subquery optimizer
FALSE Otherwise
DESCRIPTION
For index lookup-based subquery (i.e. one executed with
subselect_uniquesubquery_engine or subselect_indexsubquery_engine),
check its EXPLAIN output row should contain
"Using index" (TAB_INFO_FULL_SCAN_ON_NULL)
"Using Where" (TAB_INFO_USING_WHERE)
"Full scan on NULL key" (TAB_INFO_FULL_SCAN_ON_NULL)
and set appropriate flags in join_tab->packed_info.
*/
bool is_having_subq_predicates(Item *having)
static void save_index_subquery_explain_info(JOIN_TAB *join_tab, Item* where)
{
if (having->type() == Item::FUNC_ITEM)
join_tab->packed_info= TAB_INFO_HAVE_VALUE;
if (join_tab->table->used_keys.is_set(join_tab->ref.key))
join_tab->packed_info |= TAB_INFO_USING_INDEX;
if (where)
join_tab->packed_info |= TAB_INFO_USING_WHERE;
for (uint i = 0; i < join_tab->ref.key_parts; i++)
{
if (((Item_func *) having)->functype() == Item_func::ISNOTNULLTEST_FUNC)
return TRUE;
if (((Item_func *) having)->functype() == Item_func::TRIG_COND_FUNC)
if (join_tab->ref.cond_guards[i])
{
having= ((Item_func*)having)->arguments()[0];
if (((Item_func *) having)->functype() == Item_func::ISNOTNULLTEST_FUNC)
return TRUE;
join_tab->packed_info |= TAB_INFO_FULL_SCAN_ON_NULL;
break;
}
return TRUE;
}
return FALSE;
}
/*
global select optimisation.
return 0 - success
@ -1017,51 +1033,47 @@ JOIN::optimize()
if (join_tab[0].type == JT_EQ_REF &&
join_tab[0].ref.items[0]->name == in_left_expr_name)
{
if (test_in_subselect(&where))
{
join_tab[0].type= JT_UNIQUE_SUBQUERY;
error= 0;
DBUG_RETURN(unit->item->
change_engine(new
subselect_uniquesubquery_engine(thd,
join_tab,
unit->item,
where)));
}
remove_subq_pushed_predicates(&where);
save_index_subquery_explain_info(join_tab, where);
join_tab[0].type= JT_UNIQUE_SUBQUERY;
error= 0;
DBUG_RETURN(unit->item->
change_engine(new
subselect_uniquesubquery_engine(thd,
join_tab,
unit->item,
where)));
}
else if (join_tab[0].type == JT_REF &&
join_tab[0].ref.items[0]->name == in_left_expr_name)
{
if (test_in_subselect(&where))
{
join_tab[0].type= JT_INDEX_SUBQUERY;
error= 0;
DBUG_RETURN(unit->item->
change_engine(new
subselect_indexsubquery_engine(thd,
join_tab,
unit->item,
where,
0)));
}
remove_subq_pushed_predicates(&where);
save_index_subquery_explain_info(join_tab, where);
join_tab[0].type= JT_INDEX_SUBQUERY;
error= 0;
DBUG_RETURN(unit->item->
change_engine(new
subselect_indexsubquery_engine(thd,
join_tab,
unit->item,
where,
NULL,
0)));
}
} else if (join_tab[0].type == JT_REF_OR_NULL &&
join_tab[0].ref.items[0]->name == in_left_expr_name &&
is_having_subq_predicates(having))
having->name == in_having_cond)
{
join_tab[0].type= JT_INDEX_SUBQUERY;
error= 0;
if ((conds= remove_additional_cond(conds)))
join_tab->info= "Using index; Using where";
else
join_tab->info= "Using index";
conds= remove_additional_cond(conds);
save_index_subquery_explain_info(join_tab, conds);
DBUG_RETURN(unit->item->
change_engine(new subselect_indexsubquery_engine(thd,
join_tab,
unit->item,
conds,
having,
1)));
}
@ -2557,9 +2569,7 @@ typedef struct key_field_t { // Used when finding key fields
when val IS NULL.
*/
bool null_rejecting;
/* TRUE<=> This ref access is an outer subquery reference access */
bool outer_ref;
bool *cond_guard; /* See KEYUSE::cond_guard */
} KEY_FIELD;
/* Values in optimize */
@ -2858,7 +2868,7 @@ add_key_field(KEY_FIELD **key_fields,uint and_level, Item_func *cond,
cond->functype() == Item_func::MULT_EQUAL_FUNC) &&
((*value)->type() == Item::FIELD_ITEM) &&
((Item_field*)*value)->field->maybe_null());
(*key_fields)->outer_ref= FALSE;
(*key_fields)->cond_guard= NULL;
(*key_fields)++;
}
@ -2955,8 +2965,9 @@ add_key_fields(JOIN *join, KEY_FIELD **key_fields, uint *and_level,
}
/*
Subquery optimization: check if the encountered condition is one
added by condition push down into subquery.
Subquery optimization: Conditions that are pushed down into subqueries
are wrapped into Item_func_trig_cond. We process the wrapped condition
but need to set cond_guard for KEYUSE elements generated from it.
*/
{
if (cond->type() == Item::FUNC_ITEM &&
@ -2973,7 +2984,7 @@ add_key_fields(JOIN *join, KEY_FIELD **key_fields, uint *and_level,
sargables);
// Indicate that this ref access candidate is for subquery lookup:
for (; save != *key_fields; save++)
save->outer_ref= TRUE;
save->cond_guard= ((Item_func_trig_cond*)cond)->get_trig_var();
}
return;
}
@ -3153,7 +3164,7 @@ add_key_part(DYNAMIC_ARRAY *keyuse_array,KEY_FIELD *key_field)
keyuse.used_tables=key_field->val->used_tables();
keyuse.optimize= key_field->optimize & KEY_OPTIMIZE_REF_OR_NULL;
keyuse.null_rejecting= key_field->null_rejecting;
keyuse.outer_ref= key_field->outer_ref;
keyuse.cond_guard= key_field->cond_guard;
VOID(insert_dynamic(keyuse_array,(gptr) &keyuse));
}
}
@ -4992,7 +5003,8 @@ static bool create_ref_for_key(JOIN *join, JOIN_TAB *j, KEYUSE *org_keyuse,
if (!(j->ref.key_buff= (byte*) thd->calloc(ALIGN_SIZE(length)*2)) ||
!(j->ref.key_copy= (store_key**) thd->alloc((sizeof(store_key*) *
(keyparts+1)))) ||
!(j->ref.items= (Item**) thd->alloc(sizeof(Item*)*keyparts)))
!(j->ref.items= (Item**) thd->alloc(sizeof(Item*)*keyparts)) ||
!(j->ref.cond_guards= (bool**) thd->alloc(sizeof(uint*)*keyparts)))
{
DBUG_RETURN(TRUE);
}
@ -5007,6 +5019,8 @@ static bool create_ref_for_key(JOIN *join, JOIN_TAB *j, KEYUSE *org_keyuse,
if (ftkey)
{
j->ref.items[0]=((Item_func*)(keyuse->val))->key_item();
/* Predicates pushed down into subquery can't be used FT access */
j->ref.cond_guards[0]= NULL;
if (keyuse->used_tables)
DBUG_RETURN(TRUE); // not supported yet. SerG
@ -5023,6 +5037,7 @@ static bool create_ref_for_key(JOIN *join, JOIN_TAB *j, KEYUSE *org_keyuse,
uint maybe_null= test(keyinfo->key_part[i].null_bit);
j->ref.items[i]=keyuse->val; // Save for cond removal
j->ref.cond_guards[i]= keyuse->cond_guard;
if (keyuse->null_rejecting)
j->ref.null_rejecting |= 1 << i;
keyuse_uses_no_tables= keyuse_uses_no_tables && !keyuse->used_tables;
@ -7653,7 +7668,7 @@ change_cond_ref_to_const(THD *thd, I_List<COND_CMP> *save_list,
SYNOPSIS
remove_additional_cond()
conds - condition for processing
conds Condition for processing
RETURN VALUES
new conditions
@ -10911,7 +10926,9 @@ int rr_sequential(READ_RECORD *info);
int init_read_record_seq(JOIN_TAB *tab)
{
tab->read_record.read_record= rr_sequential;
return tab->read_record.file->ha_rnd_init(1);
if (tab->read_record.file->ha_rnd_init(1))
return 1;
return (*tab->read_record.read_record)(&tab->read_record);
}
static int
@ -14819,6 +14836,24 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
if (tab->info)
item_list.push_back(new Item_string(tab->info,strlen(tab->info),cs));
else if (tab->packed_info & TAB_INFO_HAVE_VALUE)
{
if (tab->packed_info & TAB_INFO_USING_INDEX)
extra.append(STRING_WITH_LEN("; Using index"));
if (tab->packed_info & TAB_INFO_USING_WHERE)
extra.append(STRING_WITH_LEN("; Using where"));
if (tab->packed_info & TAB_INFO_FULL_SCAN_ON_NULL)
extra.append(STRING_WITH_LEN("; Full scan on NULL key"));
/* Skip initial "; "*/
const char *str= extra.ptr();
uint32 len= extra.length();
if (len)
{
str += 2;
len -= 2;
}
item_list.push_back(new Item_string(str, len, cs));
}
else
{
if (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_UNION ||
@ -14877,6 +14912,15 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
}
if (distinct & test_all_bits(used_tables,thd->used_tables))
extra.append(STRING_WITH_LEN("; Distinct"));
for (uint part= 0; part < tab->ref.key_parts; part++)
{
if (tab->ref.cond_guards[part])
{
extra.append(STRING_WITH_LEN("; Full scan on NULL key"));
break;
}
}
/* Skip initial "; "*/
const char *str= extra.ptr();