用Mysql语句实现报表，写一个函数，给定三个参数，年份，月份，该月份的第几周，计算出该周的起止日期。如果该月1号不在周一，则从1号所在周几到本周周日结束。如果该月最后一天不在周日，则显示最后一天对应的周几

。函数实现如下：

DELIMITER //
CREATE FUNCTION get_week_range(year INT, month INT, week INT)
RETURNS VARCHAR(100)
BEGIN
    DECLARE start_date DATE;
    DECLARE end_date DATE;
    DECLARE first_day_of_month DATE;
    DECLARE last_day_of_month DATE;
    DECLARE first_weekday INT;
    DECLARE last_weekday INT;
    SET first_day_of_month = CONCAT(year, '-', month, '-01');
    SET last_day_of_month = LAST_DAY(first_day_of_month);
    SET first_weekday = DAYOFWEEK(first_day_of_month);
    SET last_weekday = DAYOFWEEK(last_day_of_month);
    IF first_weekday > 2 THEN
        SET start_date = DATE_SUB(first_day_of_month, INTERVAL first_weekday-2 DAY);
    ELSE
        SET start_date = first_day_of_month;
    END IF;
    IF last_weekday < 7 THEN
        SET end_date = DATE_ADD(last_day_of_month, INTERVAL 7-last_weekday DAY);
    ELSE
        SET end_date = last_day_of_month;
    END IF;
    RETURN CONCAT(start_date, ' ~ ', end_date);
END //
DELIMITER ;

函数的参数为年份、月份和该月份的第几周，返回值为该周的起止日期（格式为'YYYY-MM-DD ~ YYYY-MM-DD'）。

使用示例：

SELECT get_week_range(2022, 2, 3); -- 返回'2022-01-17 ~ 2022-01-23'
SELECT get_week_range(2022, 2, 4); -- 返回'2022-01-24 ~ 2022-01-31'
SELECT get_week_range(2022, 12, 1); -- 返回'2022-11-28 ~ 2022-12-04'
SELECT get_week_range(2022, 12, 5); -- 返回'2022-12-26 ~ 2022-12-31'