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.

1 files changed, 11 insertions, 8 deletions

diff --git a/sql/item_timefunc.h b/sql/item_timefunc.h
index d5d3efeeab4..e79c62e6ffb 100644
--- a/sql/item_timefunc.h
+++ b/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