Possible solution with passing tests

But it seems we should not need to divide by 1M at this point and rather deal with this deeper in the stack, where there is ns specific support.

Author: craigtaverner

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/operator/lookup/QueryList.java

@@ -219,7 +219,7 @@ public static QueryList dateNanosTermQueryList(MappedFieldType field, SearchExec
             null,
             field instanceof RangeFieldMapper.RangeFieldType rangeFieldType
                 ? offset -> rangeFieldType.dateTimeFormatter().formatNanos(block.getLong(offset))
-                : block::getLong
+                : i -> block.getLong(i) / 1000_000
         );
     }
 

x-pack/plugin/esql/qa/testFixtures/src/main/java/org/elasticsearch/xpack/esql/CsvTestsDataLoader.java

@@ -83,6 +83,8 @@ public class CsvTestsDataLoader {
     private static final TestDataset SAMPLE_DATA_TS_NANOS = SAMPLE_DATA.withIndex("sample_data_ts_nanos")
         .withData("sample_data_ts_nanos.csv")
         .withTypeMapping(Map.of("@timestamp", "date_nanos"));
+    private static final TestDataset SAMPLE_DATA_TS_NANOS_LOOKUP = SAMPLE_DATA_TS_NANOS.withIndex("sample_data_ts_nanos_lookup")
+        .withSetting("lookup-settings.json");
     private static final TestDataset MISSING_IP_SAMPLE_DATA = new TestDataset("missing_ip_sample_data");
     private static final TestDataset SAMPLE_DATA_PARTIAL_MAPPING = new TestDataset("partial_mapping_sample_data");
     private static final TestDataset SAMPLE_DATA_NO_MAPPING = new TestDataset(
@@ -162,6 +164,7 @@ public class CsvTestsDataLoader {
         Map.entry(SAMPLE_DATA_STR.indexName, SAMPLE_DATA_STR),
         Map.entry(SAMPLE_DATA_TS_LONG.indexName, SAMPLE_DATA_TS_LONG),
         Map.entry(SAMPLE_DATA_TS_NANOS.indexName, SAMPLE_DATA_TS_NANOS),
+        Map.entry(SAMPLE_DATA_TS_NANOS_LOOKUP.indexName, SAMPLE_DATA_TS_NANOS_LOOKUP),
         Map.entry(MISSING_IP_SAMPLE_DATA.indexName, MISSING_IP_SAMPLE_DATA),
         Map.entry(CLIENT_IPS.indexName, CLIENT_IPS),
         Map.entry(CLIENT_IPS_LOOKUP.indexName, CLIENT_IPS_LOOKUP),

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

@@ -1742,3 +1742,26 @@ max:long
 3450233
 8268153
 ;
+
+###############################################
+# LOOKUP JOIN on date_nanos field
+###############################################
+
+joinDateNanos
+required_capability: join_lookup_v12
+required_capability: date_nanos_type
+
+FROM sample_data_ts_nanos
+| LOOKUP JOIN sample_data_ts_nanos_lookup ON @timestamp
+| KEEP @timestamp, client_ip, event_duration, message
+;
+
+@timestamp:date_nanos | client_ip:ip | event_duration:long | message:keyword
+2023-10-23T13:55:01.543123456Z | 172.21.3.15 | 1756467 | Connected to 10.1.0.1
+2023-10-23T13:53:55.832123456Z | 172.21.3.15 | 5033755 | Connection error
+2023-10-23T13:52:55.015123456Z | 172.21.3.15 | 8268153 | Connection error
+2023-10-23T13:51:54.732123456Z | 172.21.3.15 | 725448 | Connection error
+2023-10-23T13:33:34.937123456Z | 172.21.0.5 | 1232382 | Disconnected
+2023-10-23T12:27:28.948123456Z | 172.21.2.113 | 2764889 | Connected to 10.1.0.2
+2023-10-23T12:15:03.360123456Z | 172.21.2.162 | 3450233 | Connected to 10.1.0.3
+;