Subqueries with an aggregate did not always work. Example: select (select…

Subqueries with an aggregate did not always work. Example: select (select count(*) from test where a = t.a and b = 0) from test t group by a

h2/src/main/org/h2/index/IndexCursor.java

@@ -217,6 +217,9 @@ public class IndexCursor implements Cursor {
     }
 
     public Row get() {
+        if (cursor == null) {
+            return null;
+        }
         return cursor.get();
     }
 

h2/src/main/org/h2/table/TableFilter.java

@@ -28,6 +28,7 @@ import org.h2.util.StatementBuilder;
 import org.h2.util.StringUtils;
 import org.h2.value.Value;
 import org.h2.value.ValueLong;
+import org.h2.value.ValueNull;
 
 /**
  * A table filter represents a table that is used in a query. There is one such
@@ -866,6 +867,9 @@ public class TableFilter implements ColumnResolver {
                 return v;
             }
             current = cursor.get();
+            if (current == null) {
+                return ValueNull.INSTANCE;
+            }
         }
         return current.getValue(columnId);
     }

h2/src/test/org/h2/test/db/TestCases.java

@@ -38,6 +38,7 @@ public class TestCases extends TestBase {
     }
 
     public void test() throws Exception {
+        testGroupSubquery();
         testCountDistinctNotNull();
         testDependencies();
         testConvertType();
@@ -95,6 +96,19 @@ public class TestCases extends TestBase {
         deleteDb("cases");
     }
 
+    private void testGroupSubquery() throws SQLException {
+        deleteDb("cases");
+        Connection conn = getConnection("cases");
+        Statement stat = conn.createStatement();
+        stat.execute("create table test(a int, b int)");
+        stat.execute("create index idx on test(a)");
+        stat.execute("insert into test values (1, 9), (2, 9), (3, 9)");
+        ResultSet rs = stat.executeQuery("select (select count(*) from test where a = t.a and b = 0) from test t group by a");
+        rs.next();
+        assertEquals(0, rs.getInt(1));
+        conn.close();
+    }
+
     private void testCountDistinctNotNull() throws SQLException {
         deleteDb("cases");
         Connection conn = getConnection("cases");