Ensure nested field could be used in lookup joins (#118963) (#119073)

Author: idegtiarenko

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

@@ -64,6 +64,11 @@ public class CsvTestsDataLoader {
         .withSetting("languages_lookup-settings.json");
     private static final TestsDataset LANGUAGES_LOOKUP_NON_UNIQUE_KEY = LANGUAGES_LOOKUP.withIndex("languages_lookup_non_unique_key")
         .withData("languages_non_unique_key.csv");
+    private static final TestsDataset LANGUAGES_NESTED_FIELDS = new TestsDataset(
+        "languages_nested_fields",
+        "mapping-languages_nested_fields.json",
+        "languages_nested_fields.csv"
+    ).withSetting("languages_lookup-settings.json");
     private static final TestsDataset ALERTS = new TestsDataset("alerts");
     private static final TestsDataset UL_LOGS = new TestsDataset("ul_logs");
     private static final TestsDataset SAMPLE_DATA = new TestsDataset("sample_data");
@@ -116,6 +121,7 @@ public class CsvTestsDataLoader {
         Map.entry(LANGUAGES.indexName, LANGUAGES),
         Map.entry(LANGUAGES_LOOKUP.indexName, LANGUAGES_LOOKUP),
         Map.entry(LANGUAGES_LOOKUP_NON_UNIQUE_KEY.indexName, LANGUAGES_LOOKUP_NON_UNIQUE_KEY),
+        Map.entry(LANGUAGES_NESTED_FIELDS.indexName, LANGUAGES_NESTED_FIELDS),
         Map.entry(UL_LOGS.indexName, UL_LOGS),
         Map.entry(SAMPLE_DATA.indexName, SAMPLE_DATA),
         Map.entry(MV_SAMPLE_DATA.indexName, MV_SAMPLE_DATA),

x-pack/plugin/esql/qa/testFixtures/src/main/resources/data/languages_nested_fields.csv

@@ -0,0 +1,5 @@
+_id:integer,language.id:integer,language.name:text,language.code:keyword
+1,1,English,EN
+2,2,French,FR
+3,3,Spanish,ES
+4,4,German,DE

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

@@ -416,6 +416,55 @@ language_code:integer | language_name:keyword       | country:keyword
 8                     | Mv-Lang2                    | Mv-Land2
 ;
 
+###########################################################################
+# nested filed join behavior with languages_nested_fields index
+###########################################################################
+
+joinOnNestedField
+required_capability: join_lookup_v8
+
+FROM employees
+| WHERE 10000 < emp_no AND emp_no < 10006
+| EVAL language.id = emp_no % 10
+| LOOKUP JOIN languages_nested_fields ON language.id
+| SORT emp_no
+| KEEP emp_no, language.id, language.name
+;
+
+emp_no:integer | language.id:integer | language.name:text
+10001          | 1                   | English
+10002          | 2                   | French
+10003          | 3                   | Spanish
+10004          | 4                   | German
+10005          | 5                   | null
+;
+
+
+joinOnNestedFieldRow
+required_capability: join_lookup_v8
+
+ROW language.code = "EN"
+| LOOKUP JOIN languages_nested_fields ON language.code
+| KEEP language.id, language.code, language.name.keyword
+;
+
+language.id:integer | language.code:keyword | language.name.keyword:keyword
+1                   | EN                    | English
+;
+
+
+joinOnNestedNestedFieldRow
+required_capability: join_lookup_v8
+
+ROW language.name.keyword = "English"
+| LOOKUP JOIN languages_nested_fields ON language.name.keyword
+| KEEP language.id, language.name, language.name.keyword
+;
+
+language.id:integer | language.name:text | language.name.keyword:keyword
+1                   | English            | English
+;
+
 ###############################################
 # Tests with clientips_lookup index
 ###############################################

x-pack/plugin/esql/qa/testFixtures/src/main/resources/mapping-languages_nested_fields.json

@@ -0,0 +1,22 @@
+{
+  "properties" : {
+    "language" : {
+      "properties" : {
+        "id": {
+          "type": "integer"
+        },
+        "name": {
+          "type": "text",
+          "fields": {
+            "keyword": {
+              "type": "keyword"
+            }
+          }
+        },
+        "code": {
+          "type": "keyword"
+        }
+      }
+    }
+  }
+}