[SPARK-14402][SQL] initcap UDF doesn't match Hive/Oracle behavior in lowercasing rest of string

## What changes were proposed in this pull request?

Current, SparkSQL `initCap` is using `toTitleCase` function. However, `UTF8String.toTitleCase` implementation changes only the first letter and just copy the other letters: e.g. sParK --> SParK. This is the correct implementation `toTitleCase`.
```
hive> select initcap('sParK');
Spark
```
```
scala> sql("select initcap('sParK')").head
res0: org.apache.spark.sql.Row = [SParK]
```

This PR updates the implementation of `initcap` using `toLowerCase` and `toTitleCase`.

## How was this patch tested?

Pass the Jenkins tests (including new testcase).

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #12175 from dongjoon-hyun/SPARK-14402.

1 files changed, 3 insertions, 3 deletions

diff --git a/sql/core/src/test/scala/org/apache/spark/sql/StringFunctionsSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/StringFunctionsSuite.scala
index e2090b0a83..6809f26968 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/StringFunctionsSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/StringFunctionsSuite.scala
@@ -272,12 +272,12 @@ class StringFunctionsSuite extends QueryTest with SharedSQLContext {
   }
 
   test("initcap function") {
-    val df = Seq(("ab", "a B")).toDF("l", "r")
+    val df = Seq(("ab", "a B", "sParK")).toDF("x", "y", "z")
     checkAnswer(
-      df.select(initcap($"l"), initcap($"r")), Row("Ab", "A B"))
+      df.select(initcap($"x"), initcap($"y"), initcap($"z")), Row("Ab", "A B", "Spark"))
 
     checkAnswer(
-      df.selectExpr("InitCap(l)", "InitCap(r)"), Row("Ab", "A B"))
+      df.selectExpr("InitCap(x)", "InitCap(y)", "InitCap(z)"), Row("Ab", "A B", "Spark"))
   }
 
   test("number format function") {