[SPARK-17117][SQL] 1 / NULL should not fail analysis

## What changes were proposed in this pull request?
This patch fixes the problem described in SPARK-17117, i.e. "SELECT 1 / NULL" throws an analysis exception:

```
org.apache.spark.sql.AnalysisException: cannot resolve '(1 / NULL)' due to data type mismatch: differing types in '(1 / NULL)' (int and null).
```

The problem is that division type coercion did not take null type into account.

## How was this patch tested?
A unit test for the type coercion, and a few end-to-end test cases using SQLQueryTestSuite.

Author: petermaxlee <petermaxlee@gmail.com>

Closes #14695 from petermaxlee/SPARK-17117.

1 files changed, 5 insertions, 2 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala
index 021952e716..21e96aaf53 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala
@@ -543,11 +543,14 @@ object TypeCoercion {
       // Decimal and Double remain the same
       case d: Divide if d.dataType == DoubleType => d
       case d: Divide if d.dataType.isInstanceOf[DecimalType] => d
-      case Divide(left, right) if isNumeric(left) && isNumeric(right) =>
+      case Divide(left, right) if isNumericOrNull(left) && isNumericOrNull(right) =>
         Divide(Cast(left, DoubleType), Cast(right, DoubleType))
     }
 
-    private def isNumeric(ex: Expression): Boolean = ex.dataType.isInstanceOf[NumericType]
+    private def isNumericOrNull(ex: Expression): Boolean = {
+      // We need to handle null types in case a query contains null literals.
+      ex.dataType.isInstanceOf[NumericType] || ex.dataType == NullType
+    }
   }
 
   /**