Fix PPL eval command string concatenation with + operator

core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java

@@ -689,7 +689,17 @@ void populate() {
       registerOperator(AND, SqlStdOperatorTable.AND);
       registerOperator(OR, SqlStdOperatorTable.OR);
       registerOperator(NOT, SqlStdOperatorTable.NOT);
-      registerOperator(ADD, SqlStdOperatorTable.PLUS);
+
+      // Register ADD (+ symbol) for numeric addition
+      register(
+          ADD,
+          (RexBuilder builder, RexNode... args) -> builder.makeCall(SqlStdOperatorTable.PLUS, args),
+          new PPLTypeChecker.PPLFamilyTypeChecker(SqlTypeFamily.NUMERIC, SqlTypeFamily.NUMERIC));
+
+      // Register ADD (+ symbol) for string concatenation
+      registerOperator(ADD, SqlStdOperatorTable.CONCAT);
+
+      // Register ADDFUNCTION for numeric addition only
       registerOperator(ADDFUNCTION, SqlStdOperatorTable.PLUS);
       registerOperator(SUBTRACT, SqlStdOperatorTable.MINUS);
       registerOperator(SUBTRACTFUNCTION, SqlStdOperatorTable.MINUS);

integ-test/src/test/java/org/opensearch/sql/calcite/remote/CalciteEvalCommandIT.java

@@ -0,0 +1,108 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.calcite.remote;
+
+import static org.opensearch.sql.legacy.TestsConstants.TEST_INDEX_BANK;
+import static org.opensearch.sql.util.MatcherUtils.rows;
+import static org.opensearch.sql.util.MatcherUtils.schema;
+import static org.opensearch.sql.util.MatcherUtils.verifyDataRows;
+import static org.opensearch.sql.util.MatcherUtils.verifySchema;
+
+import java.io.IOException;
+import org.json.JSONObject;
+import org.junit.jupiter.api.Test;
+import org.opensearch.client.Request;
+import org.opensearch.sql.ppl.PPLIntegTestCase;
+
+public class CalciteEvalCommandIT extends PPLIntegTestCase {
+
+  @Override
+  public void init() throws Exception {
+    super.init();
+    enableCalcite();
+
+    loadIndex(Index.BANK);
+
+    // Create test data for string concatenation
+    Request request1 = new Request("PUT", "/test_eval/_doc/1?refresh=true");
+    request1.setJsonEntity("{\"name\": \"Alice\", \"age\": 25, \"title\": \"Engineer\"}");
+    client().performRequest(request1);
+
+    Request request2 = new Request("PUT", "/test_eval/_doc/2?refresh=true");
+    request2.setJsonEntity("{\"name\": \"Bob\", \"age\": 30, \"title\": \"Manager\"}");
+    client().performRequest(request2);
+
+    Request request3 = new Request("PUT", "/test_eval/_doc/3?refresh=true");
+    request3.setJsonEntity("{\"name\": \"Charlie\", \"age\": null, \"title\": \"Analyst\"}");
+    client().performRequest(request3);
+  }
+
+  @Test
+  public void testEvalStringConcatenation() throws IOException {
+    JSONObject result = executeQuery("source=test_eval | eval greeting = 'Hello ' + name");
+    verifySchema(
+        result,
+        schema("name", "string"),
+        schema("title", "string"),
+        schema("age", "bigint"),
+        schema("greeting", "string"));
+    verifyDataRows(
+        result,
+        rows("Alice", "Engineer", 25, "Hello Alice"),
+        rows("Bob", "Manager", 30, "Hello Bob"),
+        rows("Charlie", "Analyst", null, "Hello Charlie"));
+  }
+
+  @Test
+  public void testEvalStringConcatenationWithNullField() throws IOException {
+    JSONObject result =
+        executeQuery(
+            "source=test_eval | eval age_desc = 'Age: ' + CAST(age AS STRING) | fields name, age,"
+                + " age_desc");
+    verifySchema(
+        result, schema("name", "string"), schema("age", "bigint"), schema("age_desc", "string"));
+    verifyDataRows(
+        result,
+        rows("Alice", 25, "Age: 25"),
+        rows("Bob", 30, "Age: 30"),
+        rows("Charlie", null, null));
+  }
+
+  @Test
+  public void testEvalStringConcatenationWithLiterals() throws IOException {
+    JSONObject result =
+        executeQuery(
+            "source=test_eval | eval full_info = 'Name: ' + name + ', Title: ' + title | fields"
+                + " name, title, full_info");
+    verifySchema(
+        result, schema("name", "string"), schema("title", "string"), schema("full_info", "string"));
+    verifyDataRows(
+        result,
+        rows("Alice", "Engineer", "Name: Alice, Title: Engineer"),
+        rows("Bob", "Manager", "Name: Bob, Title: Manager"),
+        rows("Charlie", "Analyst", "Name: Charlie, Title: Analyst"));
+  }
+
+  @Test
+  public void testEvalStringConcatenationWithExistingData() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval full_name = firstname + ' ' + lastname | head 3 | fields"
+                    + " firstname, lastname, full_name",
+                TEST_INDEX_BANK));
+    verifySchema(
+        result,
+        schema("firstname", "string"),
+        schema("lastname", "string"),
+        schema("full_name", "string"));
+    verifyDataRows(
+        result,
+        rows("Amber JOHnny", "Duke Willmington", "Amber JOHnny Duke Willmington"),
+        rows("Hattie", "Bond", "Hattie Bond"),
+        rows("Nanette", "Bates", "Nanette Bates"));
+  }
+}