[fix](fe) Reject conflicting path partition columns

fe/fe-core/src/main/java/org/apache/doris/tablefunction/ExternalFileTableValuedFunction.java

@@ -481,6 +481,11 @@ private void fillColumns(InternalService.PFetchTableSchemaResult result) {
         // HACK(tsy): path columns are all treated as STRING type now, after BE supports reading all columns
         //  types by all format readers from file meta, maybe reading path columns types from BE then.
         for (String colName : pathPartitionKeys) {
+            String colLowerName = colName.toLowerCase();
+            if (!columnLowerNames.add(colLowerName)) {
+                throw new NotSupportedException(
+                        "Path partition column conflicts with an existing column: " + colName);
+            }
             columns.add(new Column(colName, ScalarType.createVarcharType(ScalarType.MAX_VARCHAR_LENGTH), false));
         }
     }

regression-test/data/external_table_p0/tvf/test_path_partition_column_collision/partition_col=from_path/data.csv

@@ -0,0 +1,3 @@
+partition_col,value
+from_file,1
+from_file,2

regression-test/suites/external_table_p0/tvf/test_path_partition_column_collision.groovy

@@ -0,0 +1,37 @@
+// 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_path_partition_column_collision", "p0,external") {
+    String ak = getS3AK()
+    String sk = getS3SK()
+    String s3Endpoint = getS3Endpoint()
+    String bucket = context.config.otherConfigs.get("s3BucketName")
+
+    test {
+        sql """
+            desc function s3(
+                "URI" = "https://${bucket}.${s3Endpoint}/regression/tvf/test_path_partition_column_collision/partition_col=from_path/data.csv",
+                "s3.access_key" = "${ak}",
+                "s3.secret_key" = "${sk}",
+                "FORMAT" = "csv_with_names",
+                "column_separator" = ",",
+                "use_path_style" = "false", -- aliyun does not support path_style
+                "path_partition_keys" = "partition_col");
+        """
+        exception "Path partition column conflicts with an existing column: partition_col"
+    }
+}