MDEV-4861 TIME/DATETIME arithmetics does not preserve INTERVAL precision

Adding tests only.

The problem was earlier fixed by 
MDEV-4724 Some temporal functions do not preserve microseconds 

mysql-test/r/func_time.result

@@ -2228,6 +2228,29 @@ SELECT CONVERT_TZ('2001-01-01 10:20:30.12','+00:00','+01:00');
 CONVERT_TZ('2001-01-01 10:20:30.12','+00:00','+01:00')
 2001-01-01 11:20:30.12
 #
+# MDEV-4861 TIME/DATETIME arithmetics does not preserve INTERVAL precision
+#
+CREATE TABLE t1 (t0 TIME);
+INSERT INTO t1 VALUES ('00:00:00');
+SELECT t0 + INTERVAL 1.1 SECOND FROM t1;
+t0 + INTERVAL 1.1 SECOND
+00:00:01.1
+CREATE TABLE t2 AS SELECT t0 + INTERVAL 1.1 SECOND FROM t1;
+SHOW COLUMNS FROM t2;
+Field	Type	Null	Key	Default	Extra
+t0 + INTERVAL 1.1 SECOND	time(1)	YES		NULL	
+DROP TABLE t1,t2;
+CREATE TABLE t1 (t0 DATETIME);
+INSERT INTO t1 VALUES ('2001-01-01 00:00:00');
+SELECT t0 + INTERVAL 1.1 SECOND FROM t1;
+t0 + INTERVAL 1.1 SECOND
+2001-01-01 00:00:01.1
+CREATE TABLE t2 AS SELECT t0 + INTERVAL 1.1 SECOND FROM t1;
+SHOW COLUMNS FROM t2;
+Field	Type	Null	Key	Default	Extra
+t0 + INTERVAL 1.1 SECOND	datetime(1)	YES		NULL	
+DROP TABLE t1, t2;
+#
 # MDEV-4843 Wrong data type for TIMESTAMP('2001-01-01','10:10:10')
 #
 CREATE TABLE t1 AS SELECT

mysql-test/t/func_time.test

@@ -1346,6 +1346,24 @@ SELECT DATE_ADD('2001-01-01 00:00:00', INTERVAL -1.123456 SECOND);
 SELECT DATE_ADD('2001-01-01 00:00:00', INTERVAL 'xxx' SECOND);
 SELECT CONVERT_TZ('2001-01-01 10:20:30.12','+00:00','+01:00');
 
+--echo #
+--echo # MDEV-4861 TIME/DATETIME arithmetics does not preserve INTERVAL precision
+--echo #
+CREATE TABLE t1 (t0 TIME);
+INSERT INTO t1 VALUES ('00:00:00');
+SELECT t0 + INTERVAL 1.1 SECOND FROM t1;
+CREATE TABLE t2 AS SELECT t0 + INTERVAL 1.1 SECOND FROM t1; 
+SHOW COLUMNS FROM t2;
+DROP TABLE t1,t2;
+
+CREATE TABLE t1 (t0 DATETIME);
+INSERT INTO t1 VALUES ('2001-01-01 00:00:00');
+SELECT t0 + INTERVAL 1.1 SECOND FROM t1;
+CREATE TABLE t2 AS SELECT t0 + INTERVAL 1.1 SECOND FROM t1;
+SHOW COLUMNS FROM t2;
+DROP TABLE t1, t2;
+
+
 --echo #
 --echo # MDEV-4843 Wrong data type for TIMESTAMP('2001-01-01','10:10:10')
 --echo #