MDEV-15340 Wrong result HOUR(case_expression_with_time_and_datetime)

The problem was that Item_func_hybrid_field_type::get_date() did not
convert the result to the correct data type, so MYSQL_TIME::time_type
of the get_date() result could be not in sync with field_type().

Changes:
1. Adding two new classes Datetime and Date to store MYSQL_TIMESTAMP_DATETIME
   and MYSQL_TIMESTAMP_DATE values respectively
   (in addition to earlier added class Time, for MYSQL_TIMESTAMP_TIME values).
2. Adding Item_func_hybrid_field_type::time_op().
   It performs the operation using TIME representation,
   and always returns a MYSQL_TIME value with time_type=MYSQL_TIMESTAMP_TIME.
   Implementing time_op() for all affected children classes.
3. Fixing all implementations of date_op() to perform the operation
   using strictly DATETIME representation. Now they always return a MYSQL_TIME
   value with time_type=MYSQL_TIMESTAMP_{DATE|DATETIME},
   according to the result data type.
4. Removing assignment of ltime.time_type to mysql_timestamp_type()
   from all val_xxx_from_date_op(), because now date_op() makes sure
   to return a proper MYSQL_TIME value with a good time_type (and other member)
5. Adding Item_func_hybrid_field_type::val_xxx_from_time_op().
6. Overriding Type_handler_time_common::Item_func_hybrid_field_type_val_xxx()
   to call val_xxx_from_time_op() instead of val_xxx_from_date_op().
7. Modified Item_func::get_arg0_date() to return strictly a TIME value
   if TIME_TIME_ONLY is passed, or return strictly a DATETIME value otherwise.
   If args[0] returned a value of a different temporal type,
   (for example a TIME value when TIME_TIME_ONLY was not passed,
    or a DATETIME value when TIME_TIME_ONLY was passed), the conversion
   is automatically applied.
   Earlier, get_arg0_date() did not guarantee a result in
   accordance to TIME_TIME_ONLY flag.

1 files changed, 32 insertions, 0 deletions

diff --git a/mysql-test/r/func_time.result b/mysql-test/r/func_time.result
index e710f3ac438..53f61f6644f 100644
--- a/mysql-test/r/func_time.result
+++ b/mysql-test/r/func_time.result
@@ -3351,3 +3351,35 @@ SELECT CONVERT_TZ(1, ROW(1,1), 1);
 ERROR HY000: Illegal parameter data type row for operation 'convert_tz'
 SELECT CONVERT_TZ(1, 1, ROW(1,1));
 ERROR HY000: Illegal parameter data type row for operation 'convert_tz'
+#
+# MDEV-15340 Wrong result HOUR(case_expression_with_time_and_datetime)
+#
+SET TIMESTAMP=UNIX_TIMESTAMP('2018-02-17 01:02:03');
+SELECT
+COALESCE(TIME'800:00:00', NOW()) AS c,
+HOUR(COALESCE(TIME'800:00:00',NOW())) AS hc;
+c	hc
+2018-03-22 08:00:00	8
+SELECT
+CASE WHEN TRUE THEN TIME'800:00:00' ELSE NOW() END AS c,
+HOUR(CASE WHEN TRUE THEN TIME'800:00:00' ELSE NOW() END) AS hc;
+c	hc
+2018-03-22 08:00:00	8
+SELECT
+IFNULL(TIME'800:00:00', NOW()) AS c,
+HOUR(IFNULL(TIME'800:00:00', NOW())) AS hc;
+c	hc
+2018-03-22 08:00:00	8
+SELECT
+IF(TRUE,TIME'800:00:00', NOW()) AS c,
+HOUR(IF(TRUE,TIME'800:00:00', NOW())) AS hc;
+c	hc
+2018-03-22 08:00:00	8
+SELECT
+ADDTIME(TIME'10:20:30', TIMESTAMP'2001-01-01 00:00:00') AS c1,
+ADDTIME(TIME'10:20:30', COALESCE(TIMESTAMP'2001-01-01 00:00:00',TIMESTAMP'2001-01-01 00:00:00')) AS c2,
+ADDTIME(TIME'10:20:30', DATE'2001-01-01') AS c3,
+ADDTIME(TIME'10:20:30', COALESCE(DATE'2001-01-01',TIMESTAMP'2001-01-01 00:00:00')) AS c4;
+c1	c2	c3	c4
+NULL	NULL	NULL	NULL
+SET TIMESTAMP=DEFAULT;