SPARK-2186: Spark SQL DSL support for simple aggregations such as SUM and AVG

**Description** This patch enables using the `.select()` function in SchemaRDD with functions such as `Sum`, `Count` and other.
**Testing** Unit tests added.

Author: Ximo Guanter Gonzalbez <ximo@tid.es>

Closes #1211 from edrevo/add-expression-support-in-select and squashes the following commits:

fe4a1e1 [Ximo Guanter Gonzalbez] Extend SQL DSL to functions
e1d344a [Ximo Guanter Gonzalbez] SPARK-2186: Spark SQL DSL support for simple aggregations such as SUM and AVG

1 files changed, 11 insertions, 0 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/dsl/package.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/dsl/package.scala
index 26ad4837b0..1b503b957d 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/dsl/package.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/dsl/package.scala
@@ -108,6 +108,17 @@ package object dsl {
 
     implicit def symbolToUnresolvedAttribute(s: Symbol) = analysis.UnresolvedAttribute(s.name)
 
+    def sum(e: Expression) = Sum(e)
+    def sumDistinct(e: Expression) = SumDistinct(e)
+    def count(e: Expression) = Count(e)
+    def countDistinct(e: Expression*) = CountDistinct(e)
+    def avg(e: Expression) = Average(e)
+    def first(e: Expression) = First(e)
+    def min(e: Expression) = Min(e)
+    def max(e: Expression) = Max(e)
+    def upper(e: Expression) = Upper(e)
+    def lower(e: Expression) = Lower(e)
+
     implicit class DslSymbol(sym: Symbol) extends ImplicitAttribute { def s = sym.name }
     // TODO more implicit class for literal?
     implicit class DslString(val s: String) extends ImplicitOperators {