test PG mode, null parameters and lowerBound > upperBound

h2/src/main/org/h2/expression/function/Function.java

@@ -1580,6 +1580,12 @@ public class Function extends Expression implements FunctionCall {
             // https://www.postgresql.org/docs/current/arrays.html#ARRAYS-ACCESSING
             // For historical reasons postgreSQL ignore invalid indexes
             final boolean isPG = database.getMode().getEnum() == ModeEnum.PostgreSQL;
+            if (index1 > index2) {
+                if (isPG)
+                    result = ValueArray.get(array.getComponentType(), new Value[0]);
+                else
+                    result = ValueNull.INSTANCE;
+            } else {
                 if (index1 < 0) {
                     if (isPG)
                         index1 = 0;
@@ -1592,6 +1598,7 @@ public class Function extends Expression implements FunctionCall {
                     else
                         result = ValueNull.INSTANCE;
                 }
+            }
             if (result == null)
                 result = ValueArray.get(array.getComponentType(), Arrays.copyOfRange(array.getList(), index1, index2));
             break;

h2/src/test/org/h2/test/scripts/functions/system/array-slice.sql

@@ -9,8 +9,38 @@ select array_slice(ARRAY[1, 2, 3, 4], 1, 1) = ARRAY[1];
 select array_slice(ARRAY[1, 2, 3, 4], 1, 3) = ARRAY[1, 2, 3];
 >> TRUE
 
+-- test invalid indexes
+select array_slice(ARRAY[1, 2, 3, 4], 3, 1) is null;
+>> TRUE
+
 select array_slice(ARRAY[1, 2, 3, 4], 0, 3) is null;
 >> TRUE
 
 select array_slice(ARRAY[1, 2, 3, 4], 1, 5) is null;
 >> TRUE
+
+-- in PostgreSQL, indexes are corrected
+SET MODE PostgreSQL;
+> ok
+
+select array_slice(ARRAY[1, 2, 3, 4], 3, 1) = ARRAY[];
+>> TRUE
+
+select array_slice(ARRAY[1, 2, 3, 4], 0, 3) = ARRAY[1, 2, 3];
+>> TRUE
+
+select array_slice(ARRAY[1, 2, 3, 4], 1, 5) = ARRAY[1, 2, 3, 4];
+>> TRUE
+
+SET MODE Regular;
+> ok
+
+-- null parameters
+select array_slice(null, 1, 3) is null;
+>> TRUE
+
+select array_slice(ARRAY[1, 2, 3, 4], null, 3) is null;
+>> TRUE
+
+select array_slice(ARRAY[1, 2, 3, 4], 1, null) is null;
+>> TRUE