Fixed bug#16377: result of DATE/TIME functions were compared as strings which

can lead to a wrong result.

All date/time functions has the STRING result type thus their results are
compared as strings. The string date representation allows a user to skip 
some of leading zeros. This can lead to wrong comparison result if a date/time 
function result is compared to such a string constant.

The idea behind this bug fix is to compare results of date/time functions
and data/time constants as ints, because that date/time representation is 
more exact. To achieve this the agg_cmp_type() is changed to take in the
account that a date/time field or an date/time item should be compared 
as ints.

This bug fix is partially back ported from 5.0.

The agg_cmp_type() function now accepts THD as one of parameters. 
In addition, it now checks if a date/time field/function is present in the
list. If so, it tries to coerce all constants to INT to make date/time
comparison return correct result. The field for the constant coercion is
taken from the Item_field or constructed from the Item_func. In latter case
the constructed field will be freed after conversion of all constant items.
Otherwise the result is same as before - aggregated with help of the
item_cmp_type() function.

From the Item_func_between::fix_length_and_dec() function removed the part
which was converting date/time constants to int if possible. Now this is 
done by the agg_cmp_type() function.

The new function result_as_longlong() is added to the Item class. 
It indicates that the item is a date/time item and result of it can be
compared as int. Such items are date/time fields/functions.

Correct val_int() methods are implemented for classes Item_date_typecast, 
Item_func_makedate, Item_time_typecast, Item_datetime_typecast. All these
classes are derived from Item_str_func and Item_str_func::val_int() converts
its string value to int without regard to the date/time type of these items.

Arg_comparator::set_compare_func() and Arg_comparator::set_cmp_func()
functions are changed to substitute result type of an item with the INT_RESULT
if the item is a date/time item and another item is a constant. This is done
to get a correct result of comparisons like date_time_function() = string_constant.

1 files changed, 11 insertions, 5 deletions

diff --git a/sql/field.cc b/sql/field.cc
index a64eaad7308..ec4d4b4e4f5 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -6841,7 +6841,11 @@ create_field::create_field(Field *old_field,Field *orig_field)
 bool 
 Field::set_warning(const uint level, const uint code, int cuted_increment)
 {
-  THD *thd= table->in_use;
+  /*
+    If this field was created only for type conversion purposes it
+    will have table == NULL.
+  */
+  THD *thd= table ? table->in_use : current_thd;
   if (thd->count_cuted_fields)
   {
     thd->cuted_fields+= cuted_increment;
@@ -6876,7 +6880,8 @@ Field::set_datetime_warning(const uint level, const uint code,
                             timestamp_type ts_type, int cuted_increment)
 {
   if (set_warning(level, code, cuted_increment))
-    make_truncated_value_warning(table->in_use, str, str_length, ts_type);
+    make_truncated_value_warning(table ? table->in_use : current_thd,
+                                 str, str_length, ts_type);
 }
 
 
@@ -6905,8 +6910,8 @@ Field::set_datetime_warning(const uint level, const uint code,
   {
     char str_nr[22];
     char *str_end= longlong10_to_str(nr, str_nr, -10);
-    make_truncated_value_warning(table->in_use, str_nr, str_end - str_nr, 
-                                 ts_type);
+    make_truncated_value_warning(table ? table->in_use : current_thd,
+                                 str_nr, str_end - str_nr, ts_type);
   }
 }
 
@@ -6935,7 +6940,8 @@ Field::set_datetime_warning(const uint level, const uint code,
     /* DBL_DIG is enough to print '-[digits].E+###' */
     char str_nr[DBL_DIG + 8];
     uint str_len= my_sprintf(str_nr, (str_nr, "%g", nr));
-    make_truncated_value_warning(table->in_use, str_nr, str_len, ts_type);
+    make_truncated_value_warning(table ? table->in_use : current_thd,
+                                 str_nr, str_len, ts_type);
   }
 }