[SPARK-5383][SQL] Support alias for udtfs

Add support for alias of udtfs, such as
```
select stack(2, key, value, key, value) as (a, b) from src limit 5;

select a, b from (select stack(2, key, value, key, value) as (a, b) from src) t limit 5

```

Author: wangfei <wangfei1@huawei.com>
Author: scwf <wangfei1@huawei.com>
Author: Fei Wang <wangfei1@huawei.com>

Closes #4186 from scwf/multi-alias-names and squashes the following commits:

c35e922 [wangfei] fix conflicts
adc8311 [wangfei] minor format fix
2783aed [wangfei] convert it to a Generate instead of leaving it inside of a Project clause
a87668a [wangfei] minor improvement
b25d9b3 [wangfei] resolve conflicts
d38f041 [wangfei] style fix
8cfcebf [wangfei] minor improvement
12a239e [wangfei] fix test case
050177f [wangfei] added extendedCheckRules
3d69329 [wangfei] added CheckMultiAlias to analyzer
324150d [wangfei] added multi alias node
74f5a81 [Fei Wang] imports order fix
5bc3f59 [scwf] style fix
3daec28 [scwf] support alias for udfs with multi output columns

3 files changed, 42 insertions, 3 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
index cefd70acf3..ae7f7b9feb 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
@@ -69,8 +69,9 @@ class Analyzer(catalog: Catalog,
       typeCoercionRules ++
       extendedRules : _*),
     Batch("Check Analysis", Once,
-      CheckResolution,
-      CheckAggregation),
+      CheckResolution ::
+      CheckAggregation ::
+      Nil: _*),
     Batch("AnalysisOperators", fixedPoint,
       EliminateAnalysisOperators)
   )
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/unresolved.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/unresolved.scala
index 6606028918..f35921e2a7 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/unresolved.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/unresolved.scala
@@ -128,6 +128,44 @@ case class UnresolvedStar(table: Option[String]) extends Star {
   override def toString = table.map(_ + ".").getOrElse("") + "*"
 }
 
+/**
+ * Used to assign new names to Generator's output, such as hive udtf.
+ * For example the SQL expression "stack(2, key, value, key, value) as (a, b)" could be represented
+ * as follows:
+ *  MultiAlias(stack_function, Seq(a, b))
+
+ * @param child the computation being performed
+ * @param names the names to be associated with each output of computing [[child]].
+ */
+case class MultiAlias(child: Expression, names: Seq[String])
+  extends Attribute with trees.UnaryNode[Expression] {
+
+  override def name = throw new UnresolvedException(this, "name")
+
+  override def exprId = throw new UnresolvedException(this, "exprId")
+
+  override def dataType = throw new UnresolvedException(this, "dataType")
+
+  override def nullable = throw new UnresolvedException(this, "nullable")
+
+  override def qualifiers = throw new UnresolvedException(this, "qualifiers")
+
+  override lazy val resolved = false
+
+  override def newInstance = this
+
+  override def withNullability(newNullability: Boolean) = this
+
+  override def withQualifiers(newQualifiers: Seq[String]) = this
+
+  override def withName(newName: String) = this
+
+  override def eval(input: Row = null): EvaluatedType =
+    throw new TreeNodeException(this, s"No function to evaluate expression. type: ${this.nodeName}")
+
+  override def toString: String = s"$child AS $names"
+
+}
 
 /**
  * Represents all the resolved input attributes to a given relational operator. This is used
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/namedExpressions.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/namedExpressions.scala
index f388cd5972..e6ab1fd8d7 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/namedExpressions.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/namedExpressions.scala
@@ -75,7 +75,7 @@ abstract class Attribute extends NamedExpression {
 /**
  * Used to assign a new name to a computation.
  * For example the SQL expression "1 + 1 AS a" could be represented as follows:
- *  Alias(Add(Literal(1), Literal(1), "a")()
+ *  Alias(Add(Literal(1), Literal(1)), "a")()
  *
  * Note that exprId and qualifiers are in a separate parameter list because
  * we only pattern match on child and name.