Implement ValueInterval.getSignum(), add(), and subtract()

h2/src/main/org/h2/value/ValueInterval.java

@@ -291,6 +291,23 @@ public class ValueInterval extends Value {
         return negative ? -cmp : cmp;
     }
 
+    @Override
+    public int getSignum() {
+        return negative ? -1 : leading == 0L && remaining == 0L ? 0 : 1;
+    }
+
+    @Override
+    public Value add(Value v) {
+        return DateTimeUtils.intervalFromAbsolute(getQualifier(),
+                DateTimeUtils.intervalToAbsolute(this).add(DateTimeUtils.intervalToAbsolute((ValueInterval) v)));
+    }
+
+    @Override
+    public Value subtract(Value v) {
+        return DateTimeUtils.intervalFromAbsolute(getQualifier(),
+                DateTimeUtils.intervalToAbsolute(this).subtract(DateTimeUtils.intervalToAbsolute((ValueInterval) v)));
+    }
+
     @Override
     public Value negate() {
         if (leading == 0L && remaining == 0L) {

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

@@ -28,3 +28,15 @@ select sum(v), sum(v) filter (where v >= 4) from test where v <= 10;
 
 drop table test;
 > ok
+
+create table test(v interval day to second);
+> ok
+
+insert into test values ('0 1'), ('0 2'), ('0 2'), ('0 2'), ('-0 1'), ('-0 1');
+> update count: 6
+
+select sum(v) from test;
+>> INTERVAL '0 05:00:00' DAY TO SECOND
+
+drop table test;
+> ok

h2/src/test/org/h2/test/scripts/functions/numeric/sign.sql

@@ -15,6 +15,8 @@ select sign(null) en, sign(10) e1, sign(0) e0, sign(-0.1) em1 from test;
 > null 1  0  -1
 > rows: 1
 
-
-
-
+SELECT SIGN(INTERVAL '-0-1' YEAR TO MONTH) A, SIGN(INTERVAL '0' DAY) B, SIGN(INTERVAL '1' HOUR) C;
+> A  B C
+> -- - -
+> -1 0 1
+> rows: 1