Bug#21811 Odd casting with date + INTERVAL arithmetic

- Type casting was not consequent, thus when adding a DATE type with
  a WEEK interval the result type was DATETIME and not DATE as is the
  norm.
- By changing the order of the date internal enumerations the deviant
  type casting is resolved (Item_date_add_interval::fix_length_and_dec()
  which determines result type for this operation assumes that addition
  of any interval with value <= INTERVAL_DAY to date value will result
  in date). There are two independant places to change:
  interval_names[] and interval_type.

mysql-test/r/func_date_add.result

@@ -71,3 +71,17 @@ NULL
 NULL
 NULL
 drop table t1;
+End of 4.1 tests
+SELECT CAST('2006-09-26' AS DATE) + INTERVAL 1 DAY;
+CAST('2006-09-26' AS DATE) + INTERVAL 1 DAY
+2006-09-27
+SELECT CAST('2006-09-26' AS DATE) + INTERVAL 1 MONTH;
+CAST('2006-09-26' AS DATE) + INTERVAL 1 MONTH
+2006-10-26
+SELECT CAST('2006-09-26' AS DATE) + INTERVAL 1 YEAR;
+CAST('2006-09-26' AS DATE) + INTERVAL 1 YEAR
+2007-09-26
+SELECT CAST('2006-09-26' AS DATE) + INTERVAL 1 WEEK;
+CAST('2006-09-26' AS DATE) + INTERVAL 1 WEEK
+2006-10-03
+End of 5.0 tests

mysql-test/r/func_time.result

@@ -612,7 +612,7 @@ date_add(date,INTERVAL "1 1:1:1" DAY_SECOND)
 2003-01-03 01:01:01
 select date_add(date,INTERVAL "1" WEEK) from t1;
 date_add(date,INTERVAL "1" WEEK)
-2003-01-09 00:00:00
+2003-01-09
 select date_add(date,INTERVAL "1" QUARTER) from t1;
 date_add(date,INTERVAL "1" QUARTER)
 2003-04-02
@@ -621,7 +621,7 @@ timestampadd(MINUTE, 1, date)
 2003-01-02 00:01:00
 select timestampadd(WEEK, 1, date) from t1;
 timestampadd(WEEK, 1, date)
-2003-01-09 00:00:00
+2003-01-09
 select timestampadd(SQL_TSI_SECOND, 1, date) from t1;
 timestampadd(SQL_TSI_SECOND, 1, date)
 2003-01-02 00:00:01

mysql-test/t/func_date_add.test

@@ -64,4 +64,17 @@ insert into t1 values (date_add('2000-01-04', INTERVAL NULL DAY));
 select * from t1;
 drop table t1;
 
-# End of 4.1 tests
+--echo End of 4.1 tests
+
+#
+# Bug#21811
+#
+# Make sure we end up with an appropriate
+# date format (DATE) after addition operation
+#
+SELECT CAST('2006-09-26' AS DATE) + INTERVAL 1 DAY;
+SELECT CAST('2006-09-26' AS DATE) + INTERVAL 1 MONTH;
+SELECT CAST('2006-09-26' AS DATE) + INTERVAL 1 YEAR;
+SELECT CAST('2006-09-26' AS DATE) + INTERVAL 1 WEEK;
+
+--echo End of 5.0 tests

sql/item_timefunc.cc

@@ -2151,11 +2151,15 @@ bool Item_date_add_interval::eq(const Item *item, bool binary_cmp) const
           (date_sub_interval == other->date_sub_interval));
 }
 
+/*
+   'interval_names' reflects the order of the enumeration interval_type.
+   See item_timefunc.h
+ */
 
 static const char *interval_names[]=
 {
-  "year", "quarter", "month", "day", "hour",
-  "minute", "week", "second", "microsecond",
+  "year", "quarter", "month", "week", "day",  
+  "hour", "minute", "second", "microsecond",
   "year_month", "day_hour", "day_minute", 
   "day_second", "hour_minute", "hour_second",
   "minute_second", "day_microsecond",

sql/item_timefunc.h

@@ -630,18 +630,21 @@ public:
 };
 
 /*
-  The following must be sorted so that simple intervals comes first.
-  (get_interval_value() depends on this)
+  'interval_type' must be sorted so that simple intervals comes first,
+  ie year, quarter, month, week, day, hour, etc. The order based on
+  interval size is also important and the intervals should be kept in a
+  large to smaller order. (get_interval_value() depends on this)
 */
 
 enum interval_type
 {
-  INTERVAL_YEAR, INTERVAL_QUARTER, INTERVAL_MONTH, INTERVAL_DAY, INTERVAL_HOUR,
-  INTERVAL_MINUTE, INTERVAL_WEEK, INTERVAL_SECOND, INTERVAL_MICROSECOND ,
-  INTERVAL_YEAR_MONTH, INTERVAL_DAY_HOUR, INTERVAL_DAY_MINUTE,
-  INTERVAL_DAY_SECOND, INTERVAL_HOUR_MINUTE, INTERVAL_HOUR_SECOND,
-  INTERVAL_MINUTE_SECOND, INTERVAL_DAY_MICROSECOND, INTERVAL_HOUR_MICROSECOND,
-  INTERVAL_MINUTE_MICROSECOND, INTERVAL_SECOND_MICROSECOND
+  INTERVAL_YEAR, INTERVAL_QUARTER, INTERVAL_MONTH, INTERVAL_WEEK, 
+  INTERVAL_DAY, INTERVAL_HOUR, INTERVAL_MINUTE, INTERVAL_SECOND, 
+  INTERVAL_MICROSECOND, INTERVAL_YEAR_MONTH, INTERVAL_DAY_HOUR, 
+  INTERVAL_DAY_MINUTE, INTERVAL_DAY_SECOND, INTERVAL_HOUR_MINUTE, 
+  INTERVAL_HOUR_SECOND, INTERVAL_MINUTE_SECOND, INTERVAL_DAY_MICROSECOND,
+  INTERVAL_HOUR_MICROSECOND, INTERVAL_MINUTE_MICROSECOND,
+  INTERVAL_SECOND_MICROSECOND
 };
 
 class Item_date_add_interval :public Item_date_func