[SPARK-14335][SQL] Describe function command returns wrong output

## What changes were proposed in this pull request?

…because some of built-in functions are not in function registry.

This fix tries to fix issues in `describe function` command where some of the outputs
still shows Hive's function because some built-in functions are not in FunctionRegistry.

The following built-in functions have been added to FunctionRegistry:
```
-
!
*
/
&
%
^
+
<
<=
<=>
=
==
>
>=
|
~
and
in
like
not
or
rlike
when
```

The following listed functions are not added, but hard coded in `commands.scala` (hvanhovell):
```
!=
<>
between
case
```
Below are the existing result of the above functions that have not been added:
```
spark-sql> describe function `!=`;
Function: <>
Class: org.apache.hadoop.hive.ql.udf.generic.GenericUDFOPNotEqual
Usage: a <> b - Returns TRUE if a is not equal to b
```
```
spark-sql> describe function `<>`;
Function: <>
Class: org.apache.hadoop.hive.ql.udf.generic.GenericUDFOPNotEqual
Usage: a <> b - Returns TRUE if a is not equal to b
```
```
spark-sql> describe function `between`;
Function: between
Class: org.apache.hadoop.hive.ql.udf.generic.GenericUDFBetween
Usage: between a [NOT] BETWEEN b AND c - evaluate if a is [not] in between b and c
```
```
spark-sql> describe function `case`;
Function: case
Class: org.apache.hadoop.hive.ql.udf.generic.GenericUDFCase
Usage: CASE a WHEN b THEN c [WHEN d THEN e]* [ELSE f] END - When a = b, returns c; when a = d, return e; else return f
```

## How was this patch tested?

Existing tests passed. Additional test cases added.

Author: Yong Tang <yong.tang.github@outlook.com>

Closes #12128 from yongtang/SPARK-14335.

1 files changed, 23 insertions, 7 deletions

diff --git a/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/SQLQuerySuite.scala b/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/SQLQuerySuite.scala
index 14a1d4cd30..d7ec85c15d 100644
--- a/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/SQLQuerySuite.scala
+++ b/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/SQLQuerySuite.scala
@@ -203,8 +203,7 @@ class SQLQuerySuite extends QueryTest with SQLTestUtils with TestHiveSingleton {
     checkAnswer(sql("SHOW functions abc.abs"), Row("abs"))
     checkAnswer(sql("SHOW functions `abc`.`abs`"), Row("abs"))
     checkAnswer(sql("SHOW functions `abc`.`abs`"), Row("abs"))
-    // TODO: Re-enable this test after we fix SPARK-14335.
-    // checkAnswer(sql("SHOW functions `~`"), Row("~"))
+    checkAnswer(sql("SHOW functions `~`"), Row("~"))
     checkAnswer(sql("SHOW functions `a function doens't exist`"), Nil)
     checkAnswer(sql("SHOW functions `weekofyea*`"), Row("weekofyear"))
     // this probably will failed if we add more function with `sha` prefixing.
@@ -236,11 +235,28 @@ class SQLQuerySuite extends QueryTest with SQLTestUtils with TestHiveSingleton {
     checkExistence(sql("describe functioN abcadf"), true,
       "Function: abcadf not found.")
 
-    // TODO: Re-enable this test after we fix SPARK-14335.
-    // checkExistence(sql("describe functioN  `~`"), true,
-    //  "Function: ~",
-    //  "Class: org.apache.hadoop.hive.ql.udf.UDFOPBitNot",
-    //  "Usage: ~ n - Bitwise not")
+    checkExistence(sql("describe functioN  `~`"), true,
+      "Function: ~",
+      "Class: org.apache.spark.sql.catalyst.expressions.BitwiseNot",
+      "Usage: To be added.")
+
+    // Hard coded describe functions
+    checkExistence(sql("describe function  `<>`"), true,
+      "Function: <>",
+      "Usage: a <> b - Returns TRUE if a is not equal to b")
+
+    checkExistence(sql("describe function  `!=`"), true,
+      "Function: !=",
+      "Usage: a != b - Returns TRUE if a is not equal to b")
+
+    checkExistence(sql("describe function  `between`"), true,
+      "Function: between",
+      "Usage: a [NOT] BETWEEN b AND c - evaluate if a is [not] in between b and c")
+
+    checkExistence(sql("describe function  `case`"), true,
+      "Function: case",
+      "Usage: CASE a WHEN b THEN c [WHEN d THEN e]* [ELSE f] END - " +
+        "When a = b, returns c; when a = d, return e; else return f")
   }
 
   test("SPARK-5371: union with null and sum") {