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Commit 8e7217e4 authored by unknown's avatar unknown
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Fix for BUG#12882 - min/max inconsistent on empty table. 

The problem was in that the MIN/MAX optimization in opt_sum_query was
replacing MIN/MAX functions with their constant argument without
taking into account that a query has no result rows.


mysql-test/r/func_group.result:
  Test for BUG#12882.
mysql-test/t/func_group.test:
  Test for BUG#12882.
sql/item_sum.cc:
  If it is known that a query has no result rows, do not call add()
  via the call to Item_sum::no_rows_in_result() which calls reset().
  Instead directly call clear() so that the MIN and MAX functions
  produce NULL when there are no result rows.
sql/opt_sum.cc:
  * Do not apply MIN/MAX optimization when the operand of MIN/MAX is
    a constant if it can't be determined whether the query has any
    result rows. The reason is that if the query has result rows,
    then the result of MIN/MAX is its constant argument, but if the
    query result is empty, then the result of MIN/MAX must be NULL
    irrespective of its argument.
  
  * The patch also simplifies a bit the branch that hadles COUNT().
parent e6f860aa
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Showing with 273 additions and 30 deletions
mysql-test/r/func_group.result
View file @ 8e7217e4
......@@ -780,3 +780,139 @@ SELECT MAX(id) FROM t1 WHERE id < 3 AND a=2 AND b=6;
MAX(id)
NULL
DROP TABLE t1;
create table t1m (a int) engine=myisam;
create table t1i (a int) engine=innodb;
create table t2m (a int) engine=myisam;
create table t2i (a int) engine=innodb;
insert into t2m values (5);
insert into t2i values (5);
select min(a) from t1m;
min(a)
NULL
select min(7) from t1m;
min(7)
NULL
select min(7) from DUAL;
min(7)
NULL
explain select min(7) from t2m join t1m;
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(7) from t2m join t1m;
min(7)
NULL
select max(a) from t1m;
max(a)
NULL
select max(7) from t1m;
max(7)
NULL
select max(7) from DUAL;
max(7)
NULL
explain select max(7) from t2m join t1m;
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(7) from t2m join t1m;
max(7)
NULL
select 1, min(a) from t1m where a=99;
1 min(a)
1 NULL
select 1, min(a) from t1m where 1=99;
1 min(a)
1 NULL
select 1, min(1) from t1m where a=99;
1 min(1)
select 1, min(1) from t1m where 1=99;
1 min(1)
1 NULL
select 1, max(a) from t1m where a=99;
1 max(a)
1 NULL
select 1, max(a) from t1m where 1=99;
1 max(a)
1 NULL
select 1, max(1) from t1m where a=99;
1 max(1)
select 1, max(1) from t1m where 1=99;
1 max(1)
1 NULL
select min(a) from t1i;
min(a)
NULL
select min(7) from t1i;
min(7)
NULL
select min(7) from DUAL;
min(7)
NULL
explain select min(7) from t2i join t1i;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2i ALL NULL NULL NULL NULL 1
1 SIMPLE t1i ALL NULL NULL NULL NULL 1
select min(7) from t2i join t1i;
min(7)
NULL
select max(a) from t1i;
max(a)
NULL
select max(7) from t1i;
max(7)
NULL
select max(7) from DUAL;
max(7)
NULL
explain select max(7) from t2i join t1i;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2i ALL NULL NULL NULL NULL 1
1 SIMPLE t1i ALL NULL NULL NULL NULL 1
select max(7) from t2i join t1i;
max(7)
NULL
select 1, min(a) from t1i where a=99;
1 min(a)
1 NULL
select 1, min(a) from t1i where 1=99;
1 min(a)
1 NULL
select 1, min(1) from t1i where a=99;
1 min(1)
1 NULL
select 1, min(1) from t1i where 1=99;
1 min(1)
1 NULL
select 1, max(a) from t1i where a=99;
1 max(a)
1 NULL
select 1, max(a) from t1i where 1=99;
1 max(a)
1 NULL
select 1, max(1) from t1i where a=99;
1 max(1)
1 NULL
select 1, max(1) from t1i where 1=99;
1 max(1)
1 NULL
explain select count(*), min(7), max(7) from t1m, t1i;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1m system NULL NULL NULL NULL 0 const row not found
1 SIMPLE t1i ALL NULL NULL NULL NULL 1
select count(*), min(7), max(7) from t1m, t1i;
count(*) min(7) max(7)
0 NULL NULL
explain select count(*), min(7), max(7) from t1m, t2i;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1m system NULL NULL NULL NULL 0 const row not found
1 SIMPLE t2i ALL NULL NULL NULL NULL 1
select count(*), min(7), max(7) from t1m, t2i;
count(*) min(7) max(7)
0 NULL NULL
explain select count(*), min(7), max(7) from t2m, t1i;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2m system NULL NULL NULL NULL 1
1 SIMPLE t1i ALL NULL NULL NULL NULL 1
select count(*), min(7), max(7) from t2m, t1i;
count(*) min(7) max(7)
0 NULL NULL
drop table t1m, t1i, t2m, t2i;
mysql-test/t/func_group.test
View file @ 8e7217e4
......@@ -527,4 +527,73 @@ INSERT INTO t1 VALUES
SELECT MAX(id) FROM t1 WHERE id < 3 AND a=2 AND b=6;
DROP TABLE t1;
#
# Bug #12882 min/max inconsistent on empty table
#
create table t1m (a int) engine=myisam;
create table t1i (a int) engine=innodb;
create table t2m (a int) engine=myisam;
create table t2i (a int) engine=innodb;
insert into t2m values (5);
insert into t2i values (5);
# test with MyISAM
select min(a) from t1m;
select min(7) from t1m;
select min(7) from DUAL;
explain select min(7) from t2m join t1m;
select min(7) from t2m join t1m;
select max(a) from t1m;
select max(7) from t1m;
select max(7) from DUAL;
explain select max(7) from t2m join t1m;
select max(7) from t2m join t1m;
select 1, min(a) from t1m where a=99;
select 1, min(a) from t1m where 1=99;
select 1, min(1) from t1m where a=99;
select 1, min(1) from t1m where 1=99;
select 1, max(a) from t1m where a=99;
select 1, max(a) from t1m where 1=99;
select 1, max(1) from t1m where a=99;
select 1, max(1) from t1m where 1=99;
# test with InnoDB
select min(a) from t1i;
select min(7) from t1i;
select min(7) from DUAL;
explain select min(7) from t2i join t1i;
select min(7) from t2i join t1i;
select max(a) from t1i;
select max(7) from t1i;
select max(7) from DUAL;
explain select max(7) from t2i join t1i;
select max(7) from t2i join t1i;
select 1, min(a) from t1i where a=99;
select 1, min(a) from t1i where 1=99;
select 1, min(1) from t1i where a=99;
select 1, min(1) from t1i where 1=99;
select 1, max(a) from t1i where a=99;
select 1, max(a) from t1i where 1=99;
select 1, max(1) from t1i where a=99;
select 1, max(1) from t1i where 1=99;
# mixed MyISAM/InnoDB test
explain select count(*), min(7), max(7) from t1m, t1i;
select count(*), min(7), max(7) from t1m, t1i;
explain select count(*), min(7), max(7) from t1m, t2i;
select count(*), min(7), max(7) from t1m, t2i;
explain select count(*), min(7), max(7) from t2m, t1i;
select count(*), min(7), max(7) from t2m, t1i;
drop table t1m, t1i, t2m, t2i;
# End of 4.1 tests
sql/item_sum.cc
View file @ 8e7217e4
......@@ -552,8 +552,8 @@ void Item_sum_hybrid::cleanup()
void Item_sum_hybrid::no_rows_in_result()
{
Item_sum::no_rows_in_result();
was_values= FALSE;
clear();
}
......
sql/opt_sum.cc
View file @ 8e7217e4
......@@ -80,6 +80,8 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
List_iterator_fast<Item> it(all_fields);
int const_result= 1;
bool recalc_const_item= 0;
longlong count= 1;
bool is_exact_count= TRUE;
table_map removed_tables= 0, outer_tables= 0, used_tables= 0;
table_map where_tables= 0;
Item *item;
......@@ -88,9 +90,13 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
if (conds)
where_tables= conds->used_tables();
/* Don't replace expression on a table that is part of an outer join */
/*
Analyze outer join dependencies, and, if possible, compute the number
of returned rows.
*/
for (TABLE_LIST *tl=tables; tl ; tl= tl->next)
{
/* Don't replace expression on a table that is part of an outer join */
if (tl->on_expr)
{
outer_tables|= tl->table->map;
......@@ -102,15 +108,31 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
WHERE t2.field IS NULL;
*/
if (tl->table->map & where_tables)
return 0;
const_result= 0;
}
else
used_tables|= tl->table->map;
/*
If the storage manager of 'tl' gives exact row count, compute the total
number of rows. If there are no outer table dependencies, this count
may be used as the real count.
*/
if (tl->table->file->table_flags() & HA_NOT_EXACT_COUNT)
is_exact_count= FALSE;
else
{
tl->table->file->info(HA_STATUS_VARIABLE | HA_STATUS_NO_LOCK);
count*= tl->table->file->records;
}
}
if (!const_result)
return 0;
/*
Iterate through item is select part and replace COUNT(), MIN() and MAX()
with constants (if possible)
Iterate through all items in the SELECT clause and replace
COUNT(), MIN() and MAX() with constants (if possible).
*/
while ((item= it++))
......@@ -122,29 +144,15 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
case Item_sum::COUNT_FUNC:
/*
If the expr in count(expr) can never be null we can change this
to the number of rows in the tables
to the number of rows in the tables if this number is exact and
there are no outer joins.
*/
if (!conds && !((Item_sum_count*) item)->args[0]->maybe_null)
{
longlong count= 1;
TABLE_LIST *table;
for (table=tables ; table ; table=table->next)
{
if (outer_tables || (table->table->file->table_flags() &
HA_NOT_EXACT_COUNT))
{
const_result= 0; // Can't optimize left join
break;
}
tables->table->file->info(HA_STATUS_VARIABLE | HA_STATUS_NO_LOCK);
count*= table->table->file->records;
}
if (!table)
if (!conds && !((Item_sum_count*) item)->args[0]->maybe_null &&
!outer_tables && is_exact_count)
{
((Item_sum_count*) item)->make_const(count);
recalc_const_item= 1;
}
}
else
const_result= 0;
break;
......@@ -210,12 +218,27 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
}
removed_tables|= table->map;
}
else if (!expr->const_item()) // This is VERY seldom false
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;
}
((Item_sum_min*) item_sum)->reset();
if (!count)
{
/* If count != 1, 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;
......@@ -282,13 +305,28 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
}
removed_tables|= table->map;
}
else if (!expr->const_item()) // This is VERY seldom false
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;
}
((Item_sum_min*) item_sum)->reset();
((Item_sum_min*) item_sum)->make_const();
if (!count)
{
/* If count != 1, then we know that is_exact_count == TRUE. */
((Item_sum_max*) item_sum)->clear(); /* Set to NULL. */
}
else
((Item_sum_max*) item_sum)->reset(); /* Set to the constant value. */
((Item_sum_max*) item_sum)->make_const();
recalc_const_item= 1;
break;
}
......
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