Add exists query impl

elasticsearch/src/main/java/com/amazon/opendistroforelasticsearch/sql/elasticsearch/storage/script/filter/FilterQueryBuilder.java

@@ -20,6 +20,7 @@
 import static java.util.Collections.emptyMap;
 import static org.elasticsearch.script.Script.DEFAULT_SCRIPT_TYPE;
 
+import com.amazon.opendistroforelasticsearch.sql.elasticsearch.storage.script.filter.lucene.ExistsQuery;
 import com.amazon.opendistroforelasticsearch.sql.elasticsearch.storage.script.filter.lucene.LuceneQuery;
 import com.amazon.opendistroforelasticsearch.sql.elasticsearch.storage.script.filter.lucene.RangeQuery;
 import com.amazon.opendistroforelasticsearch.sql.elasticsearch.storage.script.filter.lucene.RangeQuery.Comparison;
@@ -60,6 +61,7 @@ public class FilterQueryBuilder extends ExpressionNodeVisitor<QueryBuilder, Obje
           .put(BuiltinFunctionName.LTE.getName(), new RangeQuery(Comparison.LTE))
           .put(BuiltinFunctionName.GTE.getName(), new RangeQuery(Comparison.GTE))
           .put(BuiltinFunctionName.LIKE.getName(), new WildcardQuery())
+          .put(BuiltinFunctionName.IS_NULL.getName(), new ExistsQuery())
           .build();
 
   /**

elasticsearch/src/main/java/com/amazon/opendistroforelasticsearch/sql/elasticsearch/storage/script/filter/lucene/ExistsQuery.java

@@ -0,0 +1,42 @@
+/*
+ *    Copyright 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License").
+ *    You may not use this file except in compliance with the License.
+ *    A copy of the License is located at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    or in the "license" file accompanying this file. This file is distributed
+ *    on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ *    express or implied. See the License for the specific language governing
+ *    permissions and limitations under the License.
+ *
+ */
+
+package com.amazon.opendistroforelasticsearch.sql.elasticsearch.storage.script.filter.lucene;
+
+import com.amazon.opendistroforelasticsearch.sql.expression.FunctionExpression;
+import com.amazon.opendistroforelasticsearch.sql.expression.ReferenceExpression;
+import org.elasticsearch.index.query.QueryBuilder;
+import org.elasticsearch.index.query.QueryBuilders;
+
+/**
+ * Lucene query that builds exists query by Elasticsearch DSL.
+ */
+public class ExistsQuery extends LuceneQuery {
+
+  @Override
+  public boolean canSupport(FunctionExpression func) {
+    return (func.getArguments().size() == 1)
+        && (func.getArguments().get(0) instanceof ReferenceExpression);
+  }
+
+  @Override
+  public QueryBuilder build(FunctionExpression func) {
+    ReferenceExpression ref = (ReferenceExpression) func.getArguments().get(0);
+    String fieldName = ref.getAttr();
+    return QueryBuilders.existsQuery(fieldName);
+  }
+
+}

elasticsearch/src/main/java/com/amazon/opendistroforelasticsearch/sql/elasticsearch/storage/script/filter/lucene/LuceneQuery.java

@@ -64,6 +64,9 @@ public QueryBuilder build(FunctionExpression func) {
    * @param literal       expr literal
    * @return            query
    */
-  protected abstract QueryBuilder doBuild(String fieldName, ExprType fieldType, ExprValue literal);
+  protected QueryBuilder doBuild(String fieldName, ExprType fieldType, ExprValue literal) {
+    throw new UnsupportedOperationException(
+        "Subclass doesn't implement this and build method either");
+  }
 
 }

elasticsearch/src/main/java/com/amazon/opendistroforelasticsearch/sql/elasticsearch/storage/script/filter/lucene/RangeQuery.java

@@ -24,7 +24,7 @@
 import org.elasticsearch.index.query.RangeQueryBuilder;
 
 /**
- * Lucene range query that builds range query for non-quality comparison.
+ * Lucene query that builds range query for non-quality comparison.
  */
 @RequiredArgsConstructor
 public class RangeQuery extends LuceneQuery {

elasticsearch/src/main/java/com/amazon/opendistroforelasticsearch/sql/elasticsearch/storage/script/filter/lucene/TermQuery.java

@@ -24,7 +24,7 @@
 import org.elasticsearch.index.query.QueryBuilders;
 
 /**
- * Lucene term query that build term query for equality comparison for different data types.
+ * Lucene query that build term query for equality comparison.
  */
 public class TermQuery extends LuceneQuery {
 

elasticsearch/src/main/java/com/amazon/opendistroforelasticsearch/sql/elasticsearch/storage/script/filter/lucene/WildcardQuery.java

@@ -22,16 +22,19 @@
 import org.elasticsearch.index.query.QueryBuilders;
 
 /**
- * Lucene wildcard query that builds DSL query.
+ * Lucene query that builds wildcard query.
  */
 public class WildcardQuery extends LuceneQuery {
 
   @Override
   protected QueryBuilder doBuild(String fieldName, ExprType fieldType, ExprValue literal) {
-    String matchText = literal.stringValue()
-                              .replace('%', '*')
-                              .replace('_', '?');
+    String matchText = convertSqlWildcardToLucene(literal.stringValue());
     return QueryBuilders.wildcardQuery(fieldName, matchText);
   }
 
+  private String convertSqlWildcardToLucene(String text) {
+    return text.replace('%', '*')
+               .replace('_', '?');
+  }
+
 }

elasticsearch/src/test/java/com/amazon/opendistroforelasticsearch/sql/elasticsearch/storage/script/filter/FilterQueryBuilderTest.java

@@ -80,8 +80,7 @@ void should_build_term_query_for_equality_expression() {
             + "}",
         buildQuery(
             dsl.equal(
-                ref("name", STRING), literal("John")))
-    );
+                ref("name", STRING), literal("John"))));
   }
 
   @Test
@@ -122,8 +121,21 @@ void should_build_wildcard_query_for_like_expression() {
             + "}",
         buildQuery(
             dsl.like(
-                ref("name", STRING), literal("%John_")))
-    );
+                ref("name", STRING), literal("%John_"))));
+  }
+
+  @Test
+  void should_build_exists_query_for_is_null_expression() {
+    assertEquals(
+        "{\n"
+            + "  \"exists\" : {\n"
+            + "    \"field\" : \"name\",\n"
+            + "    \"boost\" : 1.0\n"
+            + "  }\n"
+            + "}",
+        buildQuery(
+            dsl.isnull(
+                ref("name", STRING))));
   }
 
   @Test