Fix for bug #6914 "Problems using time()/date() output in expressions".

When we cast datetime value to DATE (TIME) type we should throw away its
time (date) part. This was not done properly if CAST() function was used
in datetime expressions.

mysql-test/r/cast.result

@@ -178,3 +178,12 @@ aaa	aa
 aab	aa
 aac	aa
 DROP TABLE t1;
+select date_add(cast('2004-12-30 12:00:00' as date), interval 0 hour);
+date_add(cast('2004-12-30 12:00:00' as date), interval 0 hour)
+2004-12-30 00:00:00
+select timediff(cast('2004-12-30 12:00:00' as time), '12:00:00');
+timediff(cast('2004-12-30 12:00:00' as time), '12:00:00')
+00:00:00
+select timediff(cast('1 12:00:00' as time), '12:00:00');
+timediff(cast('1 12:00:00' as time), '12:00:00')
+24:00:00

mysql-test/t/cast.test

@@ -108,3 +108,13 @@ SELECT a, CAST(a AS CHAR(3)) FROM t1 ORDER BY CAST(a AS CHAR(2)), a;
 SELECT a, CAST(a AS UNSIGNED) FROM t1 ORDER BY CAST(a AS CHAR) ;
 SELECT a, CAST(a AS CHAR(2)) FROM t1 ORDER BY CAST(a AS CHAR(3)), a;
 DROP TABLE t1;
+
+#
+# Test for bug #6914 "Problems using time()/date() output in expressions".
+# When we are casting datetime value to DATE/TIME we should throw away
+# time/date parts (correspondingly).
+#
+select date_add(cast('2004-12-30 12:00:00' as date), interval 0 hour);
+select timediff(cast('2004-12-30 12:00:00' as time), '12:00:00');
+# Still we should not throw away "days" part of time value
+select timediff(cast('1 12:00:00' as time), '12:00:00');

sql/item_timefunc.cc

@@ -2183,6 +2183,12 @@ String *Item_datetime_typecast::val_str(String *str)
 bool Item_time_typecast::get_time(TIME *ltime)
 {
   bool res= get_arg0_time(ltime);
+  /*
+    For MYSQL_TIMESTAMP_TIME value we can have non-zero day part,
+    which we should not lose.
+  */
+  if (ltime->time_type == MYSQL_TIMESTAMP_DATETIME)
+    ltime->year= ltime->month= ltime->day= 0;
   ltime->time_type= MYSQL_TIMESTAMP_TIME;
   return res;
 }
@@ -2206,6 +2212,7 @@ String *Item_time_typecast::val_str(String *str)
 bool Item_date_typecast::get_date(TIME *ltime, uint fuzzy_date)
 {
   bool res= get_arg0_date(ltime,1);
+  ltime->hour= ltime->minute= ltime->second= ltime->second_part= 0;
   ltime->time_type= MYSQL_TIMESTAMP_DATE;
   return res;
 }