ESQL: Allow the data type of null in filters

docs/changelog/118324.yaml

@@ -0,0 +1,6 @@
+pr: 118324
+summary: Allow the data type of `null` in filters
+area: ES|QL
+type: bug
+issues:
+  - 116351

docs/changelog/125832.yaml

@@ -0,0 +1,6 @@
+pr: 125832
+summary: "ESQL: Fix `NULL` handling in `IN` clause"
+area: ES|QL
+type: bug
+issues:
+  - 119950

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

@@ -191,3 +191,28 @@ emp_no:integer | languages:integer | height:double | x:double | y:double | z:dou
          10020 | null              | 1.41          | 1.41     | 1.41     | 40031.0  | 40031
          10021 | null              | 1.47          | 1.47     | 1.47     | 60408.0  | 60408
 ;
+
+whereNull
+FROM employees
+| WHERE NULL and emp_no <= 10021
+| SORT first_name, last_name
+| EVAL fullname = CONCAT(first_name, " ", last_name)
+| KEEP fullname, job_positions, salary, salary_change
+| limit 5
+;
+
+fullname:keyword | job_positions:keyword | salary:integer | salary_change:double
+;
+
+inConvertedNull
+required_capability: filter_in_converted_null
+FROM employees
+| WHERE emp_no in (10021, 10022, null::int)
+| KEEP emp_no, first_name, last_name
+| SORT emp_no
+;
+
+emp_no:integer | first_name:keyword | last_name:keyword   
+10021          | Ramzi              | Erde
+10022          | Shahaf             | Famili
+;

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

@@ -806,6 +806,12 @@ public enum Cap {
          */
         AGGREGATE_METRIC_DOUBLE_SORTING(AGGREGATE_METRIC_DOUBLE_FEATURE_FLAG),
 
+        /**
+         * Support for filter in converted null.
+         * See <a href="https://github.com/elastic/elasticsearch/issues/125832"> ESQL: Fix `NULL` handling in `IN` clause #125832 </a>
+         */
+        FILTER_IN_CONVERTED_NULL,
+
         /**
          * When creating constant null blocks in {@link org.elasticsearch.compute.lucene.ValuesSourceReaderOperator}, we also handed off
          * the ownership of that block - but didn't account for the fact that the caller might close it, leading to double releases

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/comparison/In.java

@@ -478,7 +478,7 @@ private Query translate(TranslatorHandler handler) {
         List<Query> queries = new ArrayList<>();
 
         for (Expression rhs : list()) {
-            if (DataType.isNull(rhs.dataType()) == false) {
+            if (Expressions.isGuaranteedNull(rhs) == false) {
                 if (needsTypeSpecificValueHandling(attribute.dataType())) {
                     // delegates to BinaryComparisons translator to ensure consistent handling of date and time values
                     // TODO:

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/analysis/VerifierTests.java

@@ -962,6 +962,33 @@ public void testPeriodAndDurationInEval() {
 
     public void testFilterNonBoolField() {
         assertEquals("1:19: Condition expression needs to be boolean, found [INTEGER]", error("from test | where emp_no"));
+
+        assertEquals(
+            "1:19: Condition expression needs to be boolean, found [KEYWORD]",
+            error("from test | where concat(first_name, \"foobar\")")
+        );
+    }
+
+    public void testFilterNullField() {
+        // `where null` should return empty result set
+        query("from test | where null");
+
+        // Value null of type `BOOLEAN`
+        query("from test | where null::boolean");
+
+        // Provide `NULL` type in `EVAL`
+        query("from t | EVAL x = null | where x");
+
+        // `to_string(null)` is of `KEYWORD` type null, resulting in `to_string(null) == "abc"` being of `BOOLEAN`
+        query("from t | where to_string(null) == \"abc\"");
+
+        // Other DataTypes can contain null values
+        assertEquals("1:19: Condition expression needs to be boolean, found [KEYWORD]", error("from test | where null::string"));
+        assertEquals("1:19: Condition expression needs to be boolean, found [INTEGER]", error("from test | where null::integer"));
+        assertEquals(
+            "1:45: Condition expression needs to be boolean, found [DATETIME]",
+            error("from test | EVAL x = null::datetime | where x")
+        );
     }
 
     public void testFilterDateConstant() {

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/predicate/operator/comparison/InTests.java

@@ -13,19 +13,25 @@
 import org.elasticsearch.geo.GeometryTestUtils;
 import org.elasticsearch.geo.ShapeTestUtils;
 import org.elasticsearch.xpack.esql.core.expression.Expression;
+import org.elasticsearch.xpack.esql.core.expression.FieldAttribute;
 import org.elasticsearch.xpack.esql.core.expression.FoldContext;
 import org.elasticsearch.xpack.esql.core.expression.Literal;
+import org.elasticsearch.xpack.esql.core.querydsl.query.TermsQuery;
 import org.elasticsearch.xpack.esql.core.tree.Source;
 import org.elasticsearch.xpack.esql.core.type.DataType;
+import org.elasticsearch.xpack.esql.core.type.EsField;
 import org.elasticsearch.xpack.esql.expression.function.AbstractFunctionTestCase;
 import org.elasticsearch.xpack.esql.expression.function.TestCaseSupplier;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.WildcardLikeTests;
+import org.elasticsearch.xpack.esql.planner.TranslatorHandler;
 import org.junit.AfterClass;
 
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Map;
+import java.util.Set;
 import java.util.function.Supplier;
 
 import static org.elasticsearch.xpack.esql.EsqlTestUtils.of;
@@ -79,6 +85,16 @@ private static Literal L(Object value) {
         return of(EMPTY, value);
     }
 
+    public void testConvertedNull() {
+        In in = new In(
+            EMPTY,
+            new FieldAttribute(Source.EMPTY, "field", new EsField("suffix", DataType.KEYWORD, Map.of(), true)),
+            Arrays.asList(ONE, new Literal(Source.EMPTY, null, randomFrom(DataType.types())), THREE)
+        );
+        var query = in.asQuery(TranslatorHandler.TRANSLATOR_HANDLER);
+        assertEquals(new TermsQuery(EMPTY, "field", Set.of(1, 3)), query);
+    }
+
     @ParametersFactory
     public static Iterable<Object[]> parameters() {
         List<TestCaseSupplier> suppliers = new ArrayList<>();