def as_sql(self):
        """
        Creates the SQL for this query. Returns the SQL string and list of
        parameters.
        """
        self.pre_sql_setup()
        if not self.query.values:
            return '', ()
        table = self.query.tables[0]
        qn = self.quote_name_unless_alias
        result = ['UPDATE %s' % qn(table)]
        result.append('SET')
        values, update_params = [], []
        for field, model, val in self.query.values:
            if hasattr(val, 'prepare_database_save'):
                val = val.prepare_database_save(field)
            else:
                val = field.get_db_prep_save(val, connection=self.connection)

            # Getting the placeholder for the field.
            if hasattr(field, 'get_placeholder'):
                placeholder = field.get_placeholder(val, self.connection)
            else:
                placeholder = '%s'

            if hasattr(val, 'evaluate'):
                val = SQLEvaluator(val, self.query, allow_joins=False)
            name = field.column
            if hasattr(val, 'as_sql'):
                sql, params = val.as_sql(qn, self.connection)
                values.append('%s = %s' % (qn(name), sql))
                update_params.extend(params)
            elif val is not None:
                values.append('%s = %s' % (qn(name), placeholder))
                update_params.append(val)
            else:
                values.append('%s = NULL' % qn(name))
        if not values:
            return '', ()
        result.append(', '.join(values))
        where, params = self.query.where.as_sql(qn=qn, connection=self.connection)
        if where:
            result.append('WHERE %s' % where)
        return ' '.join(result), tuple(update_params + params)
dataset/ETHPy150Open cloudera/hue/desktop/core/ext-py/Django-1.6.10/django/db/models/sql/compiler.py/SQLUpdateCompiler.as_sql/original