update doc.

Change-Id: Ic592678e4452f550b2c645be9cba5cac1c009b82

docs/sql-ref-ansi-compliance.md

@@ -112,12 +112,14 @@ SELECT * FROM t;
 The behavior of some SQL functions can be different under ANSI mode (`spark.sql.ansi.enabled=true`).
   - `size`: This function returns null for null input.
   - `element_at`: This function throws `ArrayIndexOutOfBoundsException` if using invalid indices. 
+  - `element_at`: This function throws `NoSuchElementException` if key does not exist in map. 
   - `elt`: This function throws `ArrayIndexOutOfBoundsException` if using invalid indices.
 
 ### SQL Operators
 
 The behavior of some SQL operators can be different under ANSI mode (`spark.sql.ansi.enabled=true`).
   - `array_col[index]`: This operator throws `ArrayIndexOutOfBoundsException` if using invalid indices.
+  - `map_col[key]`: This operator throws `NoSuchElementException` if key does not exist in map.
 
 ### SQL Keywords
 

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala

@@ -1911,7 +1911,9 @@ case class ArrayPosition(left: Expression, right: Expression)
       If `spark.sql.ansi.enabled` is set to true, it throws ArrayIndexOutOfBoundsException
       for invalid indices.
 
-    _FUNC_(map, key) - Returns value for given key, or NULL if the key is not contained in the map
+    _FUNC_(map, key) - Returns value for given key. The function returns NULL
+      if the key is not contained in the map and `spark.sql.ansi.enabled` is set to false.
+      If `spark.sql.ansi.enabled` is set to true, it throws NoSuchElementException instead.
   """,
   examples = """
     Examples: