Fixed error with single timestamp query (#1244)

Signed-off-by: vamsi-amazon <[email protected]>

Signed-off-by: vamsi-amazon <[email protected]>
(cherry picked from commit ee949cc)

Author: vamsimanohar

prometheus/src/main/java/org/opensearch/sql/prometheus/storage/querybuilder/SeriesSelectionQueryBuilder.java

@@ -37,7 +37,9 @@ public static String build(String metricName, Expression filterCondition) {
       SeriesSelectionExpressionNodeVisitor seriesSelectionExpressionNodeVisitor
           = new SeriesSelectionExpressionNodeVisitor();
       String selectorQuery = filterCondition.accept(seriesSelectionExpressionNodeVisitor, null);
-      return metricName + "{" + selectorQuery + "}";
+      if (selectorQuery != null) {
+        return metricName + "{" + selectorQuery + "}";
+      }
     }
     return metricName;
   }

prometheus/src/test/java/org/opensearch/sql/prometheus/storage/PrometheusMetricTableTest.java

@@ -305,7 +305,7 @@ void testTimeRangeResolverWithOutEndTimeInFilter() {
         new PrometheusMetricTable(client, "prometheus_http_total_requests");
 
 
-    //Both endTime and startTime are set.
+    //Only endTime is set.
     List<NamedExpression> finalProjectList = new ArrayList<>();
     finalProjectList.add(DSL.named(VALUE, DSL.ref(VALUE, STRING)));
     finalProjectList.add(DSL.named(TIMESTAMP, DSL.ref(TIMESTAMP, ExprCoreType.TIMESTAMP)));
@@ -726,6 +726,35 @@ void testImplementWithRelationAndFilter() {
     assertEquals(List.of(VALUE, TIMESTAMP), outputFields);
   }
 
+  @Test
+  void testImplementWithRelationAndTimestampFilter() {
+    List<NamedExpression> finalProjectList = new ArrayList<>();
+    finalProjectList.add(DSL.named(VALUE, DSL.ref(VALUE, STRING)));
+    finalProjectList.add(DSL.named(TIMESTAMP, DSL.ref(TIMESTAMP, ExprCoreType.TIMESTAMP)));
+    DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
+    Long endTime = new Date(System.currentTimeMillis()).getTime();
+    PrometheusMetricTable prometheusMetricTable =
+        new PrometheusMetricTable(client, "prometheus_http_total_requests");
+    LogicalPlan logicalPlan = project(indexScan("prometheus_http_total_requests",
+        DSL.lte(DSL.ref("@timestamp", ExprCoreType.TIMESTAMP),
+            DSL.literal(
+                fromObjectValue(dateFormat.format(new Date(endTime)),
+                    ExprCoreType.TIMESTAMP)))
+    ), finalProjectList, null);
+    PhysicalPlan physicalPlan = prometheusMetricTable.implement(logicalPlan);
+    assertTrue(physicalPlan instanceof ProjectOperator);
+    assertTrue(((ProjectOperator) physicalPlan).getInput() instanceof PrometheusMetricScan);
+    PrometheusQueryRequest request
+        = ((PrometheusMetricScan) ((ProjectOperator) physicalPlan).getInput()).getRequest();
+    assertEquals((3600 / 250) + "s", request.getStep());
+    assertEquals("prometheus_http_total_requests",
+        request.getPromQl());
+    List<NamedExpression> projectList = ((ProjectOperator) physicalPlan).getProjectList();
+    List<String> outputFields
+        = projectList.stream().map(NamedExpression::getName).collect(Collectors.toList());
+    assertEquals(List.of(VALUE, TIMESTAMP), outputFields);
+  }
+
   @Test
   void testOptimize() {
     PrometheusQueryRequest prometheusQueryRequest = new PrometheusQueryRequest();