Merge pull request ckan#3975 from camfindlay/patch-1

DOCS Note for sql searches with UPPERCASE column names

ckanext/datastore/logic/action.py

@@ -490,6 +490,10 @@ def datastore_search_sql(context, data_dict):
     .. note:: This action is only available when using PostgreSQL 9.X and
         using a read-only user on the database.
         It is not available in :ref:`legacy mode<legacy-mode>`.
+        
+    .. note:: When source data columns (i.e. CSV) heading names are provdied
+        in all UPPERCASE you need to double quote them in the SQL select 
+        statement to avoid returning null results.
 
     :param sql: a single SQL select statement
     :type sql: string