Fix possible 30 seconds error for timestamp with time zone median

h2/src/main/org/h2/expression/AggregateDataMedian.java

@@ -243,15 +243,19 @@ class AggregateDataMedian extends AggregateData {
             long dateSum = DateTimeUtils.absoluteDayFromDateValue(ts0.getDateValue())
                     + DateTimeUtils.absoluteDayFromDateValue(ts1.getDateValue());
             long nanos = (ts0.getTimeNanos() + ts1.getTimeNanos()) / 2;
+            int offset = ts0.getTimeZoneOffsetMins() + ts1.getTimeZoneOffsetMins();
             if ((dateSum & 1) != 0) {
                 nanos += DateTimeUtils.NANOS_PER_DAY / 2;
+            }
+            if ((offset & 1) != 0) {
+                nanos += 30L * 1000000000;
+            }
             if (nanos >= DateTimeUtils.NANOS_PER_DAY) {
                 nanos -= DateTimeUtils.NANOS_PER_DAY;
                 dateSum++;
             }
-            }
             return ValueTimestampTimeZone.fromDateValueAndNanos(DateTimeUtils.dateValueFromAbsoluteDay(dateSum / 2),
-                    nanos, (short) ((ts0.getTimeZoneOffsetMins() + ts1.getTimeZoneOffsetMins()) / 2));
+                    nanos, (short) (offset / 2));
         }
         default:
             // Just return first

h2/src/test/org/h2/test/scripts/functions/aggregate/median.sql

@@ -633,13 +633,13 @@ select median(v) from test;
 delete from test;
 > update count: 5
 
-insert into test values ('2000-01-20 20:00:00+10'), ('2000-01-21 20:00:00-09');
+insert into test values ('2000-01-20 20:00:00+10:15'), ('2000-01-21 20:00:00-09');
 > update count: 2
 
 select median(v) from test;
 > MEDIAN(V)
 > ---------------------------
-> 2000-01-21 08:00:00.0+00:30
+> 2000-01-21 08:00:30.0+00:37
 
 drop table test;
 > ok