add first sql elt test

Author: Kazantsev Maksim

spark/src/test/resources/sql-tests/expressions/string/elt.sql

@@ -0,0 +1,27 @@
+-- Licensed to the Apache Software Foundation (ASF) under one
+-- or more contributor license agreements.  See the NOTICE file
+-- distributed with this work for additional information
+-- regarding copyright ownership.  The ASF licenses this file
+-- to you under the Apache License, Version 2.0 (the
+-- "License"); you may not use this file except in compliance
+-- with the License.  You may obtain a copy of the License at
+--
+--   http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing,
+-- software distributed under the License 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.
+
+-- ConfigMatrix: parquet.enable.dictionary=false,true
+
+statement
+CREATE TABLE test_elt(a string, b string, c string, idx int) USING parquet
+
+statement
+INSERT INTO test_elt VALUES ('a', 'b', 'c', 1), ('a', 'b', '', 2), (NULL, 'b', 'c', NULL), ('a', NULL, 'c', -100), (NULL, NULL, NULL, 0)
+
+query
+SELECT elt(idx, a, b, c) FROM test_elt