[regression-test](fix)add test_ifnull. (#23956)

regression-test/data/query_p0/sql_functions/conditional_functions/test_ifnull.out

@@ -0,0 +1,4 @@
+-- This file is automatically generated. You should know what you did if you want to edit this
+-- !sql --
+1	11111.111110000	2222.22222	11111.11111	2222.22222
+

regression-test/suites/query_p0/sql_functions/conditional_functions/test_ifnull.groovy

@@ -0,0 +1,40 @@
+// 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.
+
+suite("test_ifnull") {
+	def tbName = "test_ifnull"
+	sql "DROP TABLE IF EXISTS ${tbName};"
+	sql"""
+		CREATE TABLE IF NOT EXISTS ${tbName} (
+			id int(11) NULL,
+			t_decimal DECIMALV3(26, 9) NULL,
+			test_double double NULL
+		) ENGINE = OLAP
+		DUPLICATE KEY(id)
+		DISTRIBUTED BY HASH(id) BUCKETS 1
+		PROPERTIES (
+		"replication_allocation" = "tag.location.default: 1");
+	"""
+	sql"""
+		INSERT INTO test_ifnull VALUES(1,11111.11111,2222.22222);
+	"""
+
+	qt_sql "select id,t_decimal,test_double,ifnull(t_decimal,test_double) as if_dou,ifnull(test_double,t_decimal) as if_dei from test_ifnull;"
+
+	sql "DROP TABLE ${tbName};"
+}
+