[SPARK-5550] [SQL] Support the case insensitive for UDF

SQL in HiveContext, should be case insensitive, however, the following query will fail.

```scala
udf.register("random0", ()  => { Math.random()})
assert(sql("SELECT RANDOM0() FROM src LIMIT 1").head().getDouble(0) >= 0.0)
```

Author: Cheng Hao <hao.cheng@intel.com>

Closes #4326 from chenghao-intel/udf_case_sensitive and squashes the following commits:

485cf66 [Cheng Hao] Support the case insensitive for UDF

2 files changed, 39 insertions, 1 deletions

diff --git a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveContext.scala b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveContext.scala
index f6d9027f90..50f266a4bc 100644
--- a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveContext.scala
+++ b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveContext.scala
@@ -311,7 +311,9 @@ class HiveContext(sc: SparkContext) extends SQLContext(sc) {
   // Note that HiveUDFs will be overridden by functions registered in this context.
   @transient
   override protected[sql] lazy val functionRegistry =
-    new HiveFunctionRegistry with OverrideFunctionRegistry
+    new HiveFunctionRegistry with OverrideFunctionRegistry {
+      def caseSensitive = false
+    }
 
   /* An analyzer that uses the Hive metastore. */
   @transient
diff --git a/sql/hive/src/test/scala/org/apache/spark/sql/hive/UDFSuite.scala b/sql/hive/src/test/scala/org/apache/spark/sql/hive/UDFSuite.scala
new file mode 100644
index 0000000000..85b6bc93d7
--- /dev/null
+++ b/sql/hive/src/test/scala/org/apache/spark/sql/hive/UDFSuite.scala
@@ -0,0 +1,36 @@
+/*
+ * 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.hive
+
+/* Implicits */
+
+import org.apache.spark.sql.QueryTest
+import org.apache.spark.sql.hive.test.TestHive._
+
+case class FunctionResult(f1: String, f2: String)
+
+class UDFSuite extends QueryTest {
+  test("UDF case insensitive") {
+    udf.register("random0", () => { Math.random()})
+    udf.register("RANDOM1", () => { Math.random()})
+    udf.register("strlenScala", (_: String).length + (_:Int))
+    assert(sql("SELECT RANDOM0() FROM src LIMIT 1").head().getDouble(0) >= 0.0)
+    assert(sql("SELECT RANDOm1() FROM src LIMIT 1").head().getDouble(0) >= 0.0)
+    assert(sql("SELECT strlenscala('test', 1) FROM src LIMIT 1").head().getInt(0) === 5)
+  }
+}