Fixing the name resolution in drop column

Author: kevinyu98

sql/core/src/main/scala/org/apache/spark/sql/DataFrame.scala

@@ -1257,7 +1257,8 @@ class DataFrame private[sql](
   def drop(colNames: String*): DataFrame = {
     val resolver = sqlContext.analyzer.resolver
     val remainingCols =
-      schema.filter(f => colNames.forall(n => !resolver(f.name, n))).map(f => Column(f.name))
+      schema.filter(f => colNames.forall(n => !resolver(f.name, n)))
+        .map(f => Column(UnresolvedAttribute(Seq(f.name))))
     if (remainingCols.size == this.schema.size) {
       this
     } else {

sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala

@@ -36,6 +36,12 @@ import org.apache.spark.sql.types._
 class DataFrameSuite extends QueryTest with SharedSQLContext {
   import testImplicits._
 
+  test("SPARK-12987") {
+    val df = Seq((1, 1)).toDF("a_b", "a.c")
+    val df1 = df.drop("a_b")
+    assert(df1.toString() === "[a.c: int]")
+    }
+
   test("analysis error should be eagerly reported") {
     // Eager analysis.
     withSQLConf(SQLConf.DATAFRAME_EAGER_ANALYSIS.key -> "true") {