Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/17758#discussion_r122865721
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/util/SchemaUtils.scala ---
@@ -0,0 +1,74 @@
+/*
+ * 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.
+ */
+
+package org.apache.spark.sql.util
+
+import scala.collection.mutable
+
+import org.apache.spark.sql.AnalysisException
+import org.apache.spark.sql.catalyst.analysis._
+import org.apache.spark.sql.types.StructType
+
+
+/**
+ * Utils for handling schemas.
+ *
+ * TODO: Merge this file with [[org.apache.spark.ml.util.SchemaUtils]].
+ */
+private[spark] object SchemaUtils {
+
+ /**
+ * Checks if an input schema has duplicate column names. This throws an
exception if the
+ * duplication exists.
+ *
+ * @param schema schema to check
+ * @param colType column type name, used in an exception message
+ * @param caseSensitiveAnalysis whether duplication checks should be
case sensitive or not
+ */
+ def checkSchemaColumnNameDuplication(
+ schema: StructType, colType: String, caseSensitiveAnalysis: Boolean
= false): Unit = {
+ val resolver = if (caseSensitiveAnalysis) {
+ caseSensitiveResolution
+ } else {
+ caseInsensitiveResolution
+ }
+ checkColumnNameDuplication(schema.map(_.name), colType, resolver)
+ }
+
+ /**
+ * Checks if input column names have duplicate identifiers. This throws
an exception if
+ * the duplication exists.
+ *
+ * @param colNames column names to check
+ * @param colType column type name, used in an exception message
+ * @param resolver resolver used to determine if two identifiers are
equal
+ */
+ def checkColumnNameDuplication(
+ colNames: Seq[String], colType: String, resolver: Resolver): Unit = {
+ val duplicateColumns = mutable.ArrayBuffer[String]()
+ colNames.foreach { name =>
+ val sameColNames = colNames.filter(resolver(_, name))
--- End diff --
the time complexity here is O(n^2), shall we follow the [previous
approach](https://github.com/apache/spark/pull/17758/files#diff-b3f9800839b9b9a1df9da9cbfc01adf8L191)
and make it O(n)?
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