[SPARK-5643][SQL] Add a show method to print the content of a DataFrame in tabular format.

An example:
```
year  month AVG('Adj Close) MAX('Adj Close)
1980  12    0.503218        0.595103
1981  01    0.523289        0.570307
1982  02    0.436504        0.475256
1983  03    0.410516        0.442194
1984  04    0.450090        0.483521
```

Author: Reynold Xin <rxin@databricks.com>

Closes #4416 from rxin/SPARK-5643 and squashes the following commits:

d0e0d6e [Reynold Xin] [SQL] Minor update to data source and statistics documentation.
269da83 [Reynold Xin] Updated isLocal comment.
2cf3c27 [Reynold Xin] Moved logic into optimizer.
1a04d8b [Reynold Xin] [SPARK-5643][SQL] Add a show method to print the content of a DataFrame in columnar format.

(cherry picked from commit a052ed42501fee3641348337505b6176426653c4)
Signed-off-by: Reynold Xin <rxin@databricks.com>

1 files changed, 57 insertions, 0 deletions

diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/ConvertToLocalRelationSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/ConvertToLocalRelationSuite.scala
new file mode 100644
index 0000000000..cf42d43823
--- /dev/null
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/ConvertToLocalRelationSuite.scala
@@ -0,0 +1,57 @@
+/*
+ * 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.sql.catalyst.optimizer
+
+import org.apache.spark.sql.Row
+import org.apache.spark.sql.catalyst.analysis.UnresolvedAttribute
+import org.apache.spark.sql.catalyst.dsl.plans._
+import org.apache.spark.sql.catalyst.dsl.expressions._
+import org.apache.spark.sql.catalyst.plans.PlanTest
+import org.apache.spark.sql.catalyst.plans.logical.{LocalRelation, LogicalPlan}
+import org.apache.spark.sql.catalyst.rules.RuleExecutor
+
+
+class ConvertToLocalRelationSuite extends PlanTest {
+
+  object Optimize extends RuleExecutor[LogicalPlan] {
+    val batches =
+      Batch("LocalRelation", FixedPoint(100),
+        ConvertToLocalRelation) :: Nil
+  }
+
+  test("Project on LocalRelation should be turned into a single LocalRelation") {
+    val testRelation = LocalRelation(
+      LocalRelation('a.int, 'b.int).output,
+      Row(1, 2) ::
+      Row(4, 5) :: Nil)
+
+    val correctAnswer = LocalRelation(
+      LocalRelation('a1.int, 'b1.int).output,
+      Row(1, 3) ::
+      Row(4, 6) :: Nil)
+
+    val projectOnLocal = testRelation.select(
+      UnresolvedAttribute("a").as("a1"),
+      (UnresolvedAttribute("b") + 1).as("b1"))
+
+    val optimized = Optimize(projectOnLocal.analyze)
+
+    comparePlans(optimized, correctAnswer)
+  }
+
+}