add CSV test

Author: not-napoleon

x-pack/plugin/esql/qa/testFixtures/src/main/resources/date_nanos.csv-spec

@@ -1249,3 +1249,26 @@ sv_nanos:date_nanos               | a:keyword             | b:keyword  | c:keywo
 2023-03-23T12:15:03.360103847Z | 2023-03-23T12:15:03.360Z | 2023-03-23 | 2023-03-23T12:15:03.360103847Z
 2023-03-23T12:15:03.360103847Z | 2023-03-23T12:15:03.360Z | 2023-03-23 | 2023-03-23T12:15:03.360103847Z
 ;
+
+Date Nanos Date Diff
+required_capability: date_nanos_date_diff
+required_capability: to_date_nanos
+
+FROM date_nanos
+| EVAL n = MV_MAX(nanos)
+| EVAL diff_sec = DATE_DIFF("seconds", TO_DATE_NANOS("2023-10-23T12:15:03.360103847Z"), n)
+| KEEP diff_sec, n;
+ignoreOrder:true
+
+diff_sec:integer | n:date_nanos
+5998             | 2023-10-23T13:55:01.543123456Z
+5932             | 2023-10-23T13:53:55.832987654Z
+5871             | 2023-10-23T13:52:55.015787878Z
+5811             | 2023-10-23T13:51:54.732102837Z
+4711             | 2023-10-23T13:33:34.937193000Z
+745              | 2023-10-23T12:27:28.948000000Z
+0                | 2023-10-23T12:15:03.360103847Z
+0                | 2023-10-23T12:15:03.360103847Z
+-18489600        | 2023-03-23T12:15:03.360103847Z
+-18489600        | 2023-03-23T12:15:03.360103847Z
+;

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/action/EsqlCapabilities.java

@@ -503,7 +503,10 @@ public enum Cap {
          * Support running date format function on nanosecond dates
          */
         DATE_NANOS_DATE_FORMAT(),
-
+        /**
+         * support date diff function on date nanos type, and mixed nanos/millis
+         */
+        DATE_NANOS_DATE_DIFF(),
         /**
          * DATE_PARSE supports reading timezones
          */