Support types table in lookup join docs

docs/reference/query-languages/esql/_snippets/commands/layout/lookup-join.md

@@ -42,6 +42,9 @@ results, the output will contain one row for each matching combination.
 For important information about using `LOOKUP JOIN`, refer to [Usage notes](../../../../esql/esql-lookup-join.md#usage-notes).
 ::::
 
+:::{include} ../types/lookup-join.md
+:::
+
 **Examples**
 
 **IP Threat correlation**: This query would allow you to see if any source

docs/reference/query-languages/esql/_snippets/commands/types/lookup-join.md

@@ -0,0 +1,21 @@
+% This is generated by ESQL's AbstractFunctionTestCase. Do not edit it. See ../README.md for how to regenerate it.
+
+**Supported types**
+
+| field from the left index | field from the lookup index | 
+| --- | --- | 
+| boolean | boolean |
+| byte | half_float, float, double, scaled_float, byte, short, integer, long |
+| date | date |
+| date_nanos | date_nanos |
+| double | half_float, float, double, scaled_float, byte, short, integer, long |
+| float | half_float, float, double, scaled_float, byte, short, integer, long |
+| half_float | half_float, float, double, scaled_float, byte, short, integer, long |
+| integer | half_float, float, double, scaled_float, byte, short, integer, long |
+| ip | ip |
+| keyword | keyword |
+| long | half_float, float, double, scaled_float, byte, short, integer, long |
+| scaled_float | half_float, float, double, scaled_float, byte, short, integer, long |
+| short | half_float, float, double, scaled_float, byte, short, integer, long |
+| text | keyword |
+

docs/reference/query-languages/esql/esql-lookup-join.md

@@ -142,19 +142,38 @@ Refer to the examples section of the [`LOOKUP JOIN`](/reference/query-languages/
 
 ## Prerequisites [esql-lookup-join-prereqs]
 
-To use `LOOKUP JOIN`, the following requirements must be met:
+### Index configuration
 
-* Indices used for lookups must be configured with the [`lookup` index mode](/reference/elasticsearch/index-settings/index-modules.md#index-mode-setting)
-* **Compatible data types**: The join key and join field in the lookup index must have compatible data types. This means:
-  * The data types must either be identical or be internally represented as the same type in {{esql}}
-  * Numeric types follow these compatibility rules:
-    * `short` and `byte` are compatible with `integer` (all represented as `int`)
-    * `float`, `half_float`, and `scaled_float` are compatible with `double` (all represented as `double`)
-  * For text fields: You can only use text fields as the join key on the left-hand side of the join and only if they have a `.keyword` subfield
+Indices used for lookups must be configured with the [`lookup` index mode](/reference/elasticsearch/index-settings/index-modules.md#index-mode-setting).
 
+### Data type compatibility
+
+Join keys must have compatible data types between the source and lookup indices. Types within the same compatibility group can be joined together:
+
+| Compatibility group    | Types                                                                               | Notes                                                                            |
+|------------------------|-------------------------------------------------------------------------------------|----------------------------------------------------------------------------------|
+| **Numeric family**     | `byte`, `short`, `integer`, `long`, `half_float`, `float`, `scaled_float`, `double` | All compatible                    |
+| **Keyword family**     | `keyword`, `text.keyword`                                                           | Text fields only as join key on left-hand side and must have `.keyword` subfield |
+| **Date (Exact)**       | `date`                                                                              | Must match exactly                                                               |
+| **Date Nanos (Exact)** | `date_nanos`                                                                        | Must match exactly                                                               |
+| **Boolean**            | `boolean`                                                                           | Must match exactly                                                               |
+
+```{tip}
 To obtain a join key with a compatible type, use a [conversion function](/reference/query-languages/esql/functions-operators/type-conversion-functions.md) if needed.
+```
 
-For a complete list of supported data types and their internal representations, see the [Supported Field Types documentation](/reference/query-languages/esql/limitations.md#_supported_types).
+### Unsupported Types
+
+In addition to the [{{esql}} unsupported field types](/reference/query-languages/esql/limitations.md#_unsupported_types), `LOOKUP JOIN` does not support:
+
+* `VERSION`
+* `UNSIGNED_LONG`
+* Spatial types like `GEO_POINT`, `GEO_SHAPE`
+* Temporal intervals like `DURATION`, `PERIOD`
+
+```{note}
+For a complete list of all types supported in `LOOKUP JOIN`, refer to the [`LOOKUP JOIN` supported types table](/reference/query-languages/esql/commands/processing-commands.md#esql-lookup-join).
+```
 
 ## Usage notes
 

x-pack/plugin/esql/build.gradle

@@ -226,6 +226,47 @@ tasks.named("test").configure {
   }
 }
 
+// This is similar to the test task above, but needed for the LookupJoinTypesIT which runs in the internalClusterTest task
+// and generates a types table for the LOOKUP JOIN command. It is possible in future we might have move tests that do this.
+tasks.named("internalClusterTest").configure {
+  if (buildParams.ci == false) {
+    systemProperty 'generateDocs', true
+    def injected = project.objects.newInstance(Injected)
+    // Define the folder to delete and recreate
+    def tempDir = file("build/testrun/internalClusterTest/temp/esql")
+    doFirst {
+      injected.fs.delete {
+        it.delete(tempDir)
+      }
+      // Re-create this folder so we can save a table of generated examples to extract from csv-spec tests
+      tempDir.mkdirs() // Recreate the folder
+    }
+    File snippetsFolder = file("build/testrun/internalClusterTest/temp/esql/_snippets")
+    def snippetsDocFolder = file("${rootDir}/docs/reference/query-languages/esql/_snippets")
+    def snippetsTree = fileTree(snippetsFolder).matching {
+      include "**/types/*.md"  // Recursively include all types/*.md files (effectively counting functions and operators)
+    }
+
+    doLast {
+      def snippets = snippetsTree.files.collect { it.name }
+      int countSnippets = snippets.size()
+      if (countSnippets == 0) {
+        logger.quiet("ESQL Docs: No function/operator snippets created. Skipping sync.")
+      } else {
+        logger.quiet("ESQL Docs: Found $countSnippets generated function/operator snippets to patch into docs")
+        injected.fs.sync {
+          from snippetsFolder
+          into snippetsDocFolder
+          include '**/*.md'
+          preserve {
+            include '**/*.md'
+          }
+        }
+      }
+    }
+  }
+}
+
 /****************************************************************
  *  Enable QA/rest integration tests for snapshot builds only   *
  *  TODO: Enable for all builds upon this feature release       *

x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/LookupJoinTypesIT.java

@@ -19,6 +19,8 @@
 import org.elasticsearch.xpack.core.esql.action.ColumnInfo;
 import org.elasticsearch.xpack.esql.VerificationException;
 import org.elasticsearch.xpack.esql.core.type.DataType;
+import org.elasticsearch.xpack.esql.expression.function.DocsV3Support;
+import org.elasticsearch.xpack.esql.expression.function.EsqlFunctionRegistry;
 import org.elasticsearch.xpack.esql.plan.logical.join.Join;
 import org.elasticsearch.xpack.esql.plugin.EsqlPlugin;
 import org.elasticsearch.xpack.spatial.SpatialPlugin;
@@ -36,6 +38,7 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Consumer;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
 import static org.elasticsearch.test.ESIntegTestCase.Scope.SUITE;
@@ -265,6 +268,22 @@ private static boolean existingIndex(Collection<TestConfigs> existing, DataType
         return existing.stream().anyMatch(c -> c.exists(indexName));
     }
 
+    /** This test generates documentation for the supported output types of the lookup join. */
+    public void testOutputSupportedTypes() throws Exception {
+        Map<List<DataType>, DataType> signatures = new LinkedHashMap<>();
+        for (TestConfigs configs : testConfigurations.values()) {
+            if (configs.group.equals("unsupported") || configs.group.equals("union-types")) {
+                continue;
+            }
+            for (TestConfig config : configs.configs.values()) {
+                if (config instanceof TestConfigPasses) {
+                    signatures.put(List.of(config.mainType(), config.lookupType()), null);
+                }
+            }
+        }
+        saveJoinTypes(() -> signatures);
+    }
+
     public void testLookupJoinStrings() {
         testLookupJoinTypes("strings");
     }
@@ -747,4 +766,18 @@ public void doTest() {
     private boolean isValidDataType(DataType dataType) {
         return UNDER_CONSTRUCTION.get(dataType) == null || UNDER_CONSTRUCTION.get(dataType).isEnabled();
     }
+
+    private static void saveJoinTypes(Supplier<Map<List<DataType>, DataType>> signatures) throws Exception {
+        ArrayList<EsqlFunctionRegistry.ArgSignature> args = new ArrayList<>();
+        args.add(new EsqlFunctionRegistry.ArgSignature("field from the left index", null, null, false, false));
+        args.add(new EsqlFunctionRegistry.ArgSignature("field from the lookup index", null, null, false, false));
+        DocsV3Support.CommandsDocsSupport docs = new DocsV3Support.CommandsDocsSupport(
+            "lookup-join",
+            LookupJoinTypesIT.class,
+            null,
+            args,
+            signatures
+        );
+        docs.renderDocs();
+    }
 }