[SPARK-20334][SQL] Return a better error message when correlated predicates contain aggregate expression that has mixture of outer and local references.

## What changes were proposed in this pull request?
Address a follow up in [comment](https://github.com/apache/spark/pull/16954#discussion_r105718880)
Currently subqueries with correlated predicates containing aggregate expression having mixture of outer references and local references generate a codegen error like following :

```SQL
SELECT t1a
FROM   t1
GROUP  BY 1
HAVING EXISTS (SELECT 1
               FROM  t2
               WHERE t2a < min(t1a + t2a));
```
Exception snippet.
```
Cannot evaluate expression: min((input[0, int, false] + input[4, int, false]))
	at org.apache.spark.sql.catalyst.expressions.Unevaluable$class.doGenCode(Expression.scala:226)
	at org.apache.spark.sql.catalyst.expressions.aggregate.AggregateExpression.doGenCode(interfaces.scala:87)
	at org.apache.spark.sql.catalyst.expressions.Expression$$anonfun$genCode$2.apply(Expression.scala:106)
	at org.apache.spark.sql.catalyst.expressions.Expression$$anonfun$genCode$2.apply(Expression.scala:103)
	at scala.Option.getOrElse(Option.scala:121)
	at org.apache.spark.sql.catalyst.expressions.Expression.genCode(Expression.scala:103)

```
After this PR, a better error message is issued.
```
org.apache.spark.sql.AnalysisException
Error in query: Found an aggregate expression in a correlated
predicate that has both outer and local references, which is not supported yet.
Aggregate expression: min((t1.`t1a` + t2.`t2a`)),
Outer references: t1.`t1a`,
Local references: t2.`t2a`.;
```
## How was this patch tested?
Added tests in SQLQueryTestSuite.

Author: Dilip Biswal <dbiswal@us.ibm.com>

Closes #17636 from dilipbiswal/subquery_followup1.

1 files changed, 18 insertions, 5 deletions

diff --git a/sql/core/src/test/scala/org/apache/spark/sql/SubquerySuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/SubquerySuite.scala
index 0f0199cbe2..131abf7c1e 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/SubquerySuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/SubquerySuite.scala
@@ -822,12 +822,25 @@ class SubquerySuite extends QueryTest with SharedSQLContext {
       checkAnswer(
         sql(
           """
-          | select c2
-          | from t1
-          | where exists (select *
-          |               from t2 lateral view explode(arr_c2) q as c2
-                          where t1.c1 = t2.c1)""".stripMargin),
+          | SELECT c2
+          | FROM t1
+          | WHERE EXISTS (SELECT *
+          |               FROM t2 LATERAL VIEW explode(arr_c2) q AS c2
+                          WHERE t1.c1 = t2.c1)""".stripMargin),
         Row(1) :: Row(0) :: Nil)
+
+      val msg1 = intercept[AnalysisException] {
+        sql(
+          """
+            | SELECT c1
+            | FROM t2
+            | WHERE EXISTS (SELECT *
+            |               FROM t1 LATERAL VIEW explode(t2.arr_c2) q AS c2
+            |               WHERE t1.c1 = t2.c1)
+          """.stripMargin)
+      }
+      assert(msg1.getMessage.contains(
+        "Expressions referencing the outer query are not supported outside of WHERE/HAVING"))
     }
   }