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:
  Updated result file for type casting test
mysql-test/r/func_time.result:
  Updated result file for type casting test
mysql-test/t/func_date_add.test:
  Added test for type casting when adding intervals to date.
sql/item_timefunc.cc:
  Changed order of "week" key word to match the date interval enumeration.
sql/item_timefunc.h:
  Changed the order of the enumeration to better follow interval sizes.

1 files changed, 6 insertions, 2 deletions

diff --git a/sql/item_timefunc.cc b/sql/item_timefunc.cc
index 30230005f6e..f3d7ff2dbdc 100644
--- a/sql/item_timefunc.cc
+++ b/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",