Commit 42e31f7a authored by unknown's avatar unknown
Browse files

Bug #15881: cast problems 

  The optimizer removes expressions from GROUP BY/DISTINCT
  if they happen to participate in a <expression> = <const>
  predicates of the WHERE clause (the idea being that if
  it's always equal to a constant it can't have multiple 
  values).
  However for predicates where the expression and the 
  constant item are of different result type this is not
  valid (e.g. a string column compared to 0).
  Fixed by additional check of the result types of the 
  expression and the constant and if they differ the 
  expression don't get removed from the group by list.


mysql-test/r/distinct.result:
  Bug #15881: cast problems
    - test case
mysql-test/t/distinct.test:
  Bug #15881: cast problems
    - test case
sql/sql_select.cc:
  Bug #15881: cast problems
    - can't use <expr>=<const> to remove GROUP BY/DISTINCT cols
      if they're not of the same type.
parent 5df7d39e

mysql-test/r/distinct.result

+37 −0
Original line number Diff line number Diff line
@@ -607,3 +607,40 @@ id select_type table type possible_keys key key_len ref rows Extra 
SELECT DISTINCT a,a FROM t1 WHERE b < 12 ORDER BY a;

a	a

DROP TABLE t1;

CREATE TABLE t1 (a CHAR(1));

INSERT INTO t1 VALUES('A'), (0);

SELECT a FROM t1 WHERE a=0;

a

A

0

Warnings:

Warning	1292	Truncated incorrect DOUBLE value: 'A'

SELECT DISTINCT a FROM t1 WHERE a=0;

a

A

0

Warnings:

Warning	1292	Truncated incorrect DOUBLE value: 'A'

DROP TABLE t1;

CREATE TABLE t1 (a DATE);

INSERT INTO t1 VALUES ('1972-07-29'), ('1972-02-06');

EXPLAIN SELECT (SELECT DISTINCT a FROM t1 WHERE a = '2002-08-03');

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used

2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where

EXPLAIN SELECT (SELECT DISTINCT ADDDATE(a,1) FROM t1

WHERE ADDDATE(a,1) = '2002-08-03');

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used

2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where; Using temporary

CREATE TABLE t2 (a CHAR(5) CHARACTER SET latin1 COLLATE latin1_general_ci);

INSERT INTO t2 VALUES (0xf6);

INSERT INTO t2 VALUES ('oe');

SELECT COUNT(*) FROM (SELECT DISTINCT a FROM t2) dt;

COUNT(*)

2

SELECT COUNT(*) FROM 

(SELECT DISTINCT a FROM t2 WHERE a='oe' COLLATE latin1_german2_ci) dt;

COUNT(*)

2

DROP TABLE t1, t2;

mysql-test/t/distinct.test

+21 −0
Original line number Diff line number Diff line
@@ -504,3 +504,24 @@ DROP TABLE t1; 
#DROP TABLE t1;

#DROP TABLE t2;



#

# Bug #15881: cast problems

#

CREATE TABLE t1 (a CHAR(1)); INSERT INTO t1 VALUES('A'), (0);

SELECT a FROM t1 WHERE a=0;

SELECT DISTINCT a FROM t1 WHERE a=0;

DROP TABLE t1;

CREATE TABLE t1 (a DATE);

INSERT INTO t1 VALUES ('1972-07-29'), ('1972-02-06');

EXPLAIN SELECT (SELECT DISTINCT a FROM t1 WHERE a = '2002-08-03');

EXPLAIN SELECT (SELECT DISTINCT ADDDATE(a,1) FROM t1

                WHERE ADDDATE(a,1) = '2002-08-03');

CREATE TABLE t2 (a CHAR(5) CHARACTER SET latin1 COLLATE latin1_general_ci);

INSERT INTO t2 VALUES (0xf6);

INSERT INTO t2 VALUES ('oe');



SELECT COUNT(*) FROM (SELECT DISTINCT a FROM t2) dt;

SELECT COUNT(*) FROM 

  (SELECT DISTINCT a FROM t2 WHERE a='oe' COLLATE latin1_german2_ci) dt;



DROP TABLE t1, t2;

sql/sql_select.cc

+42 −2
Original line number Diff line number Diff line
@@ -8432,6 +8432,46 @@ remove_eq_conds(THD *thd, COND *cond, Item::cond_result *cond_value) 
  return cond;					// Point at next and level

}



/* 

  Check if equality can be used in removing components of GROUP BY/DISTINCT

  

  SYNOPSIS

    test_if_equality_guarantees_uniqueness()

      l          the left comparison argument (a field if any)

      r          the right comparison argument (a const of any)

  

  DESCRIPTION    

    Checks if an equality predicate can be used to take away 

    DISTINCT/GROUP BY because it is known to be true for exactly one 

    distinct value (e.g. <expr> == <const>).

    Arguments must be of the same type because e.g. 

    <string_field> = <int_const> may match more than 1 distinct value from 

    the column. 

    We must take into consideration and the optimization done for various 

    string constants when compared to dates etc (see Item_int_with_ref) as

    well as the collation of the arguments.

  

  RETURN VALUE  

    TRUE    can be used

    FALSE   cannot be used

*/

static bool

test_if_equality_guarantees_uniqueness(Item *l, Item *r)

{

  return r->const_item() &&

    /* elements must be of the same result type */

    (r->result_type() == l->result_type() ||

    /* or dates compared to longs */

     (((l->type() == Item::FIELD_ITEM &&

        ((Item_field *)l)->field->can_be_compared_as_longlong()) ||

       (l->type() == Item::FUNC_ITEM &&

        ((Item_func *)l)->result_as_longlong())) &&

      r->result_type() == INT_RESULT))

    /* and must have the same collation if compared as strings */

    && (l->result_type() != STRING_RESULT ||

        l->collation.collation == r->collation.collation);

}



/*

  Return 1 if the item is a const value in all the WHERE clause

*/
@@ -8468,7 +8508,7 @@ const_expression_in_where(COND *cond, Item *comp_item, Item **const_item) 
    Item *right_item= ((Item_func*) cond)->arguments()[1];

    if (left_item->eq(comp_item,1))

    {

      if (right_item->const_item())

      if (test_if_equality_guarantees_uniqueness (left_item, right_item))

      {

	if (*const_item)

	  return right_item->eq(*const_item, 1);
@@ -8478,7 +8518,7 @@ const_expression_in_where(COND *cond, Item *comp_item, Item **const_item) 
    }

    else if (right_item->eq(comp_item,1))

    {

      if (left_item->const_item())

      if (test_if_equality_guarantees_uniqueness (right_item, left_item))

      {

	if (*const_item)

	  return left_item->eq(*const_item, 1);