Commit 8e7217e4 authored by unknown's avatar unknown
Browse files

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

mysql-test/r/func_group.result

+136 −0
Original line number Diff line number Diff line
@@ -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

+69 −0
Original line number Diff line number Diff line
@@ -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

+1 −1
Original line number Diff line number Diff line
@@ -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

+67 −29
Original line number Diff line number Diff line
@@ -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;

      }