update error message

Signed-off-by: Kai Huang <ahkcs@amazon.com>

Author: ahkcs

core/src/main/java/org/opensearch/sql/calcite/utils/CalciteToolsHelper.java

@@ -366,8 +366,10 @@ public RelNode visit(TableScan scan) {
             && errorMsg.contains("Error while preparing plan")
             && errorMsg.contains("WIDTH_BUCKET")) {
           throw new UnsupportedOperationException(
-              "The 'bins' parameter on timestamp fields is not supported when pushdown is"
-                  + " disabled.");
+              "The 'bins' parameter on timestamp fields requires: (1) pushdown to be enabled"
+                  + " (controlled by plugins.calcite.pushdown.enabled, enabled by default), and"
+                  + " (2) the timestamp field to be used as an aggregation bucket (e.g., 'stats"
+                  + " count() by @timestamp').");
         }
         throw Util.throwAsRuntime(e);
       }

integ-test/src/test/java/org/opensearch/sql/calcite/remote/CalciteBinCommandIT.java

@@ -1008,11 +1008,12 @@ public void testBinsOnTimeFieldWithPushdownDisabled_ShouldFail() throws IOExcept
     // @timestamp)
     String errorMessage = exception.getMessage();
     assertTrue(
-        "Expected clear error message about bins parameter not supported on timestamp fields when "
-            + "pushdown is disabled, but got: "
+        "Expected clear error message about bins parameter requirements on timestamp fields, but"
+            + " got: "
             + errorMessage,
-        errorMessage.contains(
-            "bins' parameter on timestamp fields is not supported when pushdown is disabled"));
+        errorMessage.contains("bins' parameter on timestamp fields requires")
+            && errorMessage.contains("pushdown to be enabled")
+            && errorMessage.contains("aggregation bucket"));
   }
 
   @Test