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Bug #15881: cast problems

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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.
This commit is contained in:
gkodinov/kgeorge@macbook.gmz 2007-01-05 14:02:50 +02:00
parent 47c044e418
commit a63df24a68
3 changed files with 100 additions and 2 deletions
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37
mysql-test/r/distinct.result
View File

@ -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;

21
mysql-test/t/distinct.test
View File

@ -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;

44
sql/sql_select.cc
View File

@ -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);