fix for bug #19690: ORDER BY eliminates rows from the result

Depending on the queries we use different data processing methods
and can lose some data in case of double (and decimal in 4.1) fields.

The fix consists of two parts:
1. double comparison changed, now double a is equal to double b 
if (a-b) is less than 5*0.1^(1 + max(a->decimals, b->decimals)). 
For example, if a->decimals==1, b->decimals==2, a==b if (a-b)<0.005
2. if we use a temporary table, store double values there as is 
to avoid any data conversion (rounding).


mysql-test/r/type_float.result:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - test result
mysql-test/t/type_float.test:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - test case
sql/field.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - use not_fixed flag instead of dec to check bounds.
sql/field.h:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - Field_Double::not_fixed flag introduced, which is set if dec == NOT_FIXED_DEC
      and is used in the ::store() to check bounds. 
    - new constructor introduced (with not_fixed_arg parameter).
sql/init.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - fill log_01[] array with 0.1 powers.
sql/item_cmpfunc.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - compare_real_fixed() and compare_e_real_fixed() introduced,
      they consider double a == double b if a-b is less than 'precision',
      'precision' is set to 5*0.1^(1 + max(a->decimals, b->decimals)), 
      for example, if a->decimals==1, b->decimals==2, 'precision' is 0.005
    - use the above functions if both arguments are fixed.
sql/item_cmpfunc.h:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - Arg_comparator::presision introduced.
    - Arg_comparator::compare_real_fixed(), Arg_comparator::compare_e_real_fixed() introduced.
sql/mysql_priv.h:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - log_01 array of 0.1 powers added.
sql/mysqld.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - log_01 array of 0.1 powers added.
sql/sql_select.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - if we create double field in a temporary table, set not_fixed flag
      (use proper constructor) to avoid data conversion 
      in the Field_double::store(). Otherwise we can lose some data.

1 files changed, 6 insertions, 0 deletions

diff --git a/sql/init.cc b/sql/init.cc
index 4beb8db0c6f..5e1b6532c75 100644
--- a/sql/init.cc
+++ b/sql/init.cc
@@ -45,6 +45,12 @@ void unireg_init(ulong options)
   {					/* It's used by filesort... */
     log_10[i]= nr ; nr*= 10.0;
   }
+  /* Make a tab of powers of 0.1 */
+  for (i= 0, nr= 0.1; i < array_elements(log_01); i++)
+  {
+    log_01[i]= nr;
+    nr*= 0.1;
+  }
   specialflag|=options;			/* Set options from argv */
   DBUG_VOID_RETURN;
 }