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.

mysql-test/r/func_time.result

@@ -630,3 +630,44 @@ select monthname(str_to_date(null, '%m')), monthname(str_to_date(null, '%m')),
 monthname(str_to_date(1, '%m')), monthname(str_to_date(0, '%m'));
 monthname(str_to_date(null, '%m'))	monthname(str_to_date(null, '%m'))	monthname(str_to_date(1, '%m'))	monthname(str_to_date(0, '%m'))
 NULL	NULL	January	NULL
+create table t1(f1 date, f2 time, f3 datetime);
+insert into t1 values ("2006-01-01", "12:01:01", "2006-01-01 12:01:01");
+insert into t1 values ("2006-01-02", "12:01:02", "2006-01-02 12:01:02");
+select f1 from t1 where f1 between "2006-1-1" and 20060101;
+f1
+2006-01-01
+select f1 from t1 where f1 between "2006-1-1" and "2006.1.1";
+f1
+2006-01-01
+select f1 from t1 where date(f1) between "2006-1-1" and "2006.1.1";
+f1
+2006-01-01
+select f2 from t1 where f2 between "12:1:2" and "12:2:2";
+f2
+12:01:02
+select f2 from t1 where time(f2) between "12:1:2" and "12:2:2";
+f2
+12:01:02
+select f3 from t1 where f3 between "2006-1-1 12:1:1" and "2006-1-1 12:1:2";
+f3
+2006-01-01 12:01:01
+select f3 from t1 where timestamp(f3) between "2006-1-1 12:1:1" and "2006-1-1 12:1:2";
+f3
+2006-01-01 12:01:01
+select f1 from t1 where "2006-1-1" between f1 and f3;
+f1
+2006-01-01
+select f1 from t1 where "2006-1-1" between date(f1) and date(f3);
+f1
+2006-01-01
+select f1 from t1 where "2006-1-1" between f1 and 'zzz';
+f1
+Warnings:
+Warning	1292	Truncated incorrect date value: 'zzz'
+select f1 from t1 where makedate(2006,1) between date(f1) and date(f3);
+f1
+2006-01-01
+select f1 from t1 where makedate(2006,2) between date(f1) and date(f3);
+f1
+2006-01-02
+drop table t1;