Github user yanboliang commented on a diff in the pull request:
https://github.com/apache/spark/pull/7465#discussion_r36585582
--- Diff:
mllib/src/main/scala/org/apache/spark/ml/feature/SQLTransformer.scala ---
@@ -0,0 +1,81 @@
+/*
+ * 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.ml.feature
+
+import org.apache.spark.SparkContext
+import org.apache.spark.annotation.Experimental
+import org.apache.spark.ml.param.{ParamMap, Param}
+import org.apache.spark.ml.Transformer
+import org.apache.spark.ml.util.Identifiable
+import org.apache.spark.sql.{SQLContext, DataFrame, Row}
+import org.apache.spark.sql.types.StructType
+
+/**
+ * :: Experimental ::
+ * Implements the transforms which are defined by SQL statement.
+ * Currently we only support SQL syntax like 'SELECT ... FROM __THIS__'
+ * where '__THIS__' represents the underlying table of the input dataset.
+ */
+@Experimental
+class SQLTransformer (override val uid: String) extends Transformer {
+
+ def this() = this(Identifiable.randomUID("sql"))
+
+ /**
+ * SQL statement parameter. The statement is provided in string form.
+ * @group param
+ */
+ final val statement: Param[String] = new Param[String](this,
"statement", "SQL statement")
+
+ /** @group setParam */
+ def setStatement(value: String): this.type = set(statement, value)
+
+ /** @group getParam */
+ def getStatement(): String = $(statement)
+
+ private val tableIdentifier: String = "__THIS__"
+
+ override def transform(dataset: DataFrame): DataFrame = {
+ val outputSchema = transformSchema(dataset.schema, logging = true)
+ val tableName = Identifiable.randomUID("sql")
+ dataset.registerTempTable(tableName)
+ val realStatement = $(statement).replace(tableIdentifier, tableName)
+ val additiveDF = dataset.sqlContext.sql(realStatement)
+ val rdd = dataset.rdd.zip(additiveDF.rdd).map {
--- End diff --
This will have different behavior with other transformers in ml.feature.
Other transformers will return the DataFrame which is composed of original
DataFrame and transformed DataFrame. But here if user did not use ```*```, he
will not keep existing columns in the output DataFrame.
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