[SPARK-10743][SQL] keep the name of expression if possible when do cast

Author: Wenchen Fan <cloud0fan@163.com>

Closes #8859 from cloud-fan/cast.

3 files changed, 7 insertions, 8 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/Column.scala b/sql/core/src/main/scala/org/apache/spark/sql/Column.scala
index 1f826887ac..37d559c8e4 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/Column.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/Column.scala
@@ -835,8 +835,8 @@ class Column(protected[sql] val expr: Expression) extends Logging {
    * @since 1.3.0
    */
   def cast(to: DataType): Column = expr match {
-    // Lift alias out of cast so we can support col.as("name").cast(IntegerType)
-    case Alias(childExpr, name) => Alias(Cast(childExpr, to), name)()
+    // keeps the name of expression if possible when do cast.
+    case ne: NamedExpression => UnresolvedAlias(Cast(expr, to))
     case _ => Cast(expr, to)
   }
 
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/ColumnExpressionSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/ColumnExpressionSuite.scala
index 4e988f074b..fa559c9c64 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/ColumnExpressionSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/ColumnExpressionSuite.scala
@@ -588,12 +588,6 @@ class ColumnExpressionSuite extends QueryTest with SharedSQLContext {
     }
   }
 
-  test("lift alias out of cast") {
-    compareExpressions(
-      col("1234").as("name").cast("int").expr,
-      col("1234").cast("int").as("name").expr)
-  }
-
   test("columns can be compared") {
     assert('key.desc == 'key.desc)
     assert('key.desc != 'key.asc)
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala
index 832ea02cb6..6424f1f1d9 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala
@@ -975,4 +975,9 @@ class DataFrameSuite extends QueryTest with SharedSQLContext {
       expected(except)
     )
   }
+
+  test("SPARK-10743: keep the name of expression if possible when do cast") {
+    val df = (1 to 10).map(Tuple1.apply).toDF("i").as("src")
+    assert(df.select($"src.i".cast(StringType)).columns.head === "i")
+  }
 }