Fix flaky PARTIAL/FINAL plan assertion in rateFunctionsNormalTest

assertRateQueryUsesIntermediateAggregation unconditionally required a
PARTIAL/FINAL aggregation split in the EXPLAIN output. Under randomized
data partition allocation (the SHUFFLE strategy used by
IoTDBTableAggregation2IT), all 8 devices of rate_merge_test may
occasionally land in a single DataRegion, where a SINGLE-step
aggregation is the correct plan, so the assertion failed sporadically.

Skip the PARTIAL/FINAL check when the plan scans fewer than two
distinct RegionIds; keep it whenever the data actually spans regions.

Author: JackieTien97

integration-test/src/test/java/org/apache/iotdb/relational/it/query/recent/IoTDBTableAggregationIT.java

@@ -36,6 +36,10 @@
 import java.sql.Connection;
 import java.sql.ResultSet;
 import java.sql.Statement;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 import static org.apache.iotdb.db.it.utils.TestUtils.prepareTableData;
 import static org.apache.iotdb.db.it.utils.TestUtils.tableAssertTestFail;
@@ -5901,6 +5905,13 @@ private void assertRateQueryUsesIntermediateAggregation(String query) {
       try (ResultSet resultSet = statement.executeQuery("EXPLAIN (FORMAT JSON) " + query)) {
         Assert.assertTrue(resultSet.next());
         String plan = resultSet.getString(1);
+        // The PARTIAL/FINAL split only exists when the scanned data spans multiple DataRegions.
+        // Under randomized partition allocation (e.g. the SHUFFLE strategy used by
+        // IoTDBTableAggregation2IT), all devices may occasionally land in one single region,
+        // where a SINGLE-step aggregation is the correct plan, so the check must be skipped.
+        if (countDistinctRegionIds(plan) < 2) {
+          return;
+        }
         Assert.assertTrue(
             "Expected a PARTIAL aggregation in plan: " + plan, plan.contains("PARTIAL"));
         Assert.assertTrue("Expected a FINAL aggregation in plan: " + plan, plan.contains("FINAL"));
@@ -5910,6 +5921,15 @@ private void assertRateQueryUsesIntermediateAggregation(String query) {
     }
   }
 
+  private static int countDistinctRegionIds(String plan) {
+    Set<String> regionIds = new HashSet<>();
+    Matcher matcher = Pattern.compile("\"RegionId\"\\s*:\\s*\"(\\d+)\"").matcher(plan);
+    while (matcher.find()) {
+      regionIds.add(matcher.group(1));
+    }
+    return regionIds.size();
+  }
+
   @Test
   public void rateFunctionsBoundaryTest() {
     tableResultSetEqualTest(