Make explain of ProjectOperator with alias show both name and alias info

Signed-off-by: Heng Qian <[email protected]>

core/src/main/java/org/opensearch/sql/expression/NamedExpression.java

@@ -60,6 +60,6 @@ public <T, C> T accept(ExpressionNodeVisitor<T, C> visitor, C context) {
 
   @Override
   public String toString() {
-    return getNameOrAlias();
+    return Strings.isNullOrEmpty(alias) ? name : name + " AS " + alias;
   }
 }

core/src/test/java/org/opensearch/sql/executor/ExplainTest.java

@@ -77,7 +77,7 @@ void can_explain_project_filter_table_scan() {
         new ExplainResponse(
             new ExplainResponseNode(
                 "ProjectOperator",
-                Map.of("fields", "[name, age]"),
+                Map.of("fields", "[full_name AS name, age]"),
                 singletonList(
                     new ExplainResponseNode(
                         "FilterOperator",

integ-test/src/test/java/org/opensearch/sql/legacy/ExplainIT.java

@@ -271,4 +271,20 @@ public void testContentTypeOfExplainRequestShouldBeJson() throws IOException {
 
     assertEquals("application/json; charset=UTF-8", response.getHeader("content-type"));
   }
+
+  @Test
+  public void explainAlias() throws IOException {
+
+    String expectedOutputFilePath =
+        TestUtils.getResourceFilePath("src/test/resources/expectedOutput/alias_explain.json");
+    String expectedOutput =
+        Files.toString(new File(expectedOutputFilePath), StandardCharsets.UTF_8)
+            .replaceAll("\r", "");
+
+    String result =
+        explainQuery(
+            String.format("SELECT (age + 1) AS agePlusOne FROM %s LIMIT 10", TEST_INDEX_ACCOUNT));
+    Assert.assertThat(
+        result.replaceAll("\\s+", ""), equalTo(expectedOutput.replaceAll("\\s+", "")));
+  }
 }

integ-test/src/test/resources/expectedOutput/alias_explain.json

@@ -0,0 +1,17 @@
+{
+    "root": {
+        "name": "ProjectOperator",
+        "description": {
+            "fields": "[(age+1) AS agePlusOne]"
+        },
+        "children": [
+            {
+                "name": "OpenSearchIndexScan",
+                "description": {
+                    "request": "OpenSearchQueryRequest(indexName=opensearch-sql_test_index_account,sourceBuilder={\"from\":0,\"size\":10,\"timeout\":\"1m\",\"_source\":{\"includes\":[\"age\"],\"excludes\":[]}},searchDone=false)"
+                },
+                "children": []
+            }
+        ]
+    }
+}