def field_cast_sql(self, db_type):
        if self.sql_server_ver < 2005 and db_type and db_type.lower() == 'ntext':
            return 'CAST(%s as nvarchar)'
        return '%s'
Given a column type (e.g. 'BLOB', 'VARCHAR'), returns the SQL necessary
dataset/ETHPy150Open avidal/django-pyodbc/sql_server/pyodbc/operations.py/DatabaseOperations.field_cast_sql