minor fix

Signed-off-by: Tomoyuki Morita <[email protected]>

Author: ykmr1224

core/src/main/java/org/opensearch/sql/expression/function/udf/SpanFunction.java

@@ -99,6 +99,7 @@ public Expression implement(
                         SpanFunction.class, methodName, String.class, int.class, String.class));
         return function.getImplementor().implement(translator, call, RexImpTable.NullAs.NULL);
       } else if (SqlTypeUtil.isCharacter(fieldType)) {
+        // if first argument is string, consider it as timestamp
         ScalarFunctionImpl function =
             (ScalarFunctionImpl)
                 ScalarFunctionImpl.create(

integ-test/src/test/java/org/opensearch/sql/calcite/standalone/CalciteDynamicFieldsTimechartIT.java

@@ -62,7 +62,7 @@ public void testTrendlineWithDynamicFieldWithCast() throws IOException {
     String query =
         source(
             TEST_INDEX_DYNAMIC,
-            "trendline sma(2, latency) as latency_trend" + "| fields id, latency, latency_trend");
+            "trendline sma(2, latency) as latency_trend| fields id, latency, latency_trend");
     JSONObject result = executeQuery(query);
 
     verifySchema(
@@ -94,7 +94,7 @@ public void testTrendlineSortByDynamicField() throws IOException {
         schema("latency", "int"),
         schema("latency_trend", "double"));
     verifyDataRows(
-        result, // [1,10,null],[3,40,25],[5,160,100],[2,20,90],[4,80,50]
+        result,
         rows(1, 10, null),
         rows(3, 40, 25),
         rows(5, 160, 100),