Existe uma maneira de obter o primeiro e o último dia da semana de um mês?

DELIMITER //
CREATE FUNCTION first_wdom (d DATETIME) -- First work/week day of month
RETURNS DATE DETERMINISTIC
BEGIN
  DECLARE first_dom DATE;
  SET first_dom = DATE_FORMAT(d, '%Y-%m-01');

  RETURN first_dom + INTERVAL (CASE DAYOFWEEK(first_dom)
                               WHEN 1 THEN 1
                               WHEN 7 THEN 2
                               ELSE 0
                               END) DAY;
END //
CREATE FUNCTION last_wdom (d DATETIME) -- Last work/week day of month
RETURNS DATE DETERMINISTIC
BEGIN
  DECLARE last_dom DATE;
  SET last_dom = LAST_DAY(d);

  RETURN last_dom - INTERVAL (CASE DAYOFWEEK(last_dom)
                              WHEN 1 THEN 2
                              WHEN 7 THEN 1
                              ELSE 0
                              END) DAY;
END //
DELIMITER ;

mysql> SELECT FIRST_WDOM('2011-05-10'), LAST_WDOM('2011-05-10');
+--------------------------+-------------------------+
| FIRST_WDOM('2011-05-10') | LAST_WDOM('2011-05-10') |
+--------------------------+-------------------------+
| 2011-05-02               | 2011-05-31              | 
+--------------------------+-------------------------+
1 row in set (0.01 sec)