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Fix for BUG#11185.

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The source of the problem is in Field_longlong::cmp. If 'this' is
  an unsigned number, the method casts both the current value, and
  the constant that we compare with to an unsigned number. As a
  result if the constant we compare with is a negative number, it
  wraps to some unsigned number, and the comparison is incorrect.
  
  When the optimizer chooses the "range" access method, this problem
  causes handler::read_range_next to reject the current key when the
  upper bound key is a negative number because handler::compare_key
  incorrectly considers the positive and negative keys to be equal.
  
  The current patch does not correct the source of the problem in
  Field_longlong::cmp because it is not easy to propagate sign
  information about the constant at query execution time. Instead
  the patch changes the range optimizer so that it never compares
  unsiged fields with negative constants. As an added benefit,
  queries that do such comparisons will execute faster because
  the range optimizer replaces conditions like:
  (a) (unsigned_int [< | <=] negative_constant) == FALSE
  (b) (unsigned_int [> | >=] negative_constant) == TRUE
  with the corresponding constants.
  In some cases this may even result in constant time execution.


mysql-test/r/range.result:
  - Added test for BUG#11185
  - Added missing test from 4.1. This test also tests the fix for BUG#11185.
mysql-test/t/range.test:
  - Added test for BUG#11185
  - Added missing test from 4.1. This test also tests the fix for BUG#11185.
sql/opt_range.cc:
  Added a new optimization to the range optimizer where we detect that
  an UNSIGNED field is compared with a negative constant. Depending on
  the comparison operator, we know directly that the result of the
  comparison is either TRUE or FALSE for all input values, and we need
  not check each value.
      
  This optimization is also necessary so that the index range access
  method produces correct results when comparing unsigned fields with
  negative constants.
This commit is contained in:
unknown
2005-06-23 12:08:56 +03:00
parent 902376e531 1abe8e6916
commit 1a8c334b30
3 changed files with 125 additions and 1 deletions
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29
sql/opt_range.cc
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@@ -3840,6 +3840,35 @@ get_mm_leaf(PARAM *param, COND *conf_func, Field *field, KEY_PART *key_part,
if (!(tree=new SEL_ARG(field,str,str)))
DBUG_RETURN(0); // out of memory
/*
Check if we are comparing an UNSIGNED integer with a negative constant.
In this case we know that:
(a) (unsigned_int [< | <=] negative_constant) == FALSE
(b) (unsigned_int [> | >=] negative_constant) == TRUE
In case (a) the condition is false for all values, and in case (b) it
is true for all values, so we can avoid unnecessary retrieval and condition
testing, and we also get correct comparison of unsinged integers with
negative integers (which otherwise fails because at query execution time
negative integers are cast to unsigned if compared with unsigned).
*/
Item_result field_result_type= field->result_type();
Item_result value_result_type= value->result_type();
if (field_result_type == INT_RESULT && value_result_type == INT_RESULT &&
((Field_num*)field)->unsigned_flag && !((Item_int*)value)->unsigned_flag)
{
longlong item_val= value->val_int();
if (item_val < 0)
{
if (type == Item_func::LT_FUNC || type == Item_func::LE_FUNC)
{
tree->type= SEL_ARG::IMPOSSIBLE;
DBUG_RETURN(tree);
}
if (type == Item_func::GT_FUNC || type == Item_func::GE_FUNC)
DBUG_RETURN(0);
}
}
switch (type) {
case Item_func::LT_FUNC:
if (field_is_equal_to_item(field,value))