MySQL按周統計每周數據總和，用到了WEEK，subdate，date_format，date_sub，date_add函數。

　　WEEK() 查看給定日期周數，語法：WEEK(date, mode);

　　SUBDATE() 函數做日期減法操作，語法：SUBDATE(date,INTERVAL expr unit) 和 SUBDATE(expr,days);

　　DATE_FORMAT() 函數用於以不同的格式顯示日期/時間數據，語法：DATE_FORMAT(date,format);

　　DATE_SUB() 函數從日期減去指定的時間間隔，語法：DATE_SUB(date,INTERVAL expr type);

　　DATE_ADD() 函數向日期添加指定的時間間，語法：DATE_ADD(date,INTERVAL expr type);

樣例數據：

-- 創建數據樣例表
CREATE TABLE `day_weight_tb` (
  `day_date` varchar(16) DEFAULT NULL,
  `in_weight` varchar(64) DEFAULT NULL,
  `out_weight` varchar(64) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- 插入樣例數據
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (
 
‘2018-03-10‘, ‘18.84‘, ‘74.14‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-01-21‘, ‘17.69‘, ‘25.97‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-02-01‘, ‘16.48‘, ‘10.0‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (
 
‘2019-01-29‘, ‘10.9‘, ‘74.12‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-02-13‘, ‘15.25‘, ‘16.62‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-01-12‘, ‘19.21‘, ‘95.42‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-02-14‘, ‘26.38‘, ‘20.59‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-01-24‘, ‘15.99‘, ‘16.823‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-01-13‘, ‘94.846‘, ‘56.256‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-03-03‘, ‘15.63‘, ‘12.128‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-03-12‘, ‘14.282‘, ‘24.046‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-01-16‘, ‘14.045‘, ‘11.73‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-03-08‘, ‘23.41‘, ‘23.441‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-01-31‘, ‘11.177‘, ‘4332.26‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-01-23‘, ‘11.8‘, ‘17104.49‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-03-17‘, ‘17.95‘, ‘13.81‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-03-01‘, ‘19.23‘, ‘20.43‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-02-05‘, ‘21.55‘, ‘51.0‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-02-27‘, ‘13.003‘, ‘23.32‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-03-11‘, ‘16.44‘, ‘24.44‘);
INSERT INTO `day_weight_tb` (`day_date`, `in_weight`, `out_weight`) VALUES (‘2019-02-28‘, ‘16.48‘, ‘23.4‘);

-- 創建結果表，插入統計結果
drop TABLE if exists week_count_tb;
CREATE TABLE `week_count_tb` (
  `week_day` varchar(32) DEFAULT NULL,
  `week_num` varchar(32) DEFAULT NULL,
  `in_weight` varchar(64) DEFAULT NULL,
  `out_weight` varchar(64) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

delete from week_count_tb;
INSERT INTO week_count_tb 
SELECT
    *
FROM
    (
        SELECT
            middle.week_day,
            middle.week_num,
            sum(in_weight) in_weight,
            sum(out_weight) out_weight
        FROM
            (
                SELECT
                    subdate(
                        date_sub(day_date, INTERVAL 1 DAY),
                        date_format(date_sub(day_date, INTERVAL 1 DAY),‘%w‘) - 7) week_day,
                    WEEK (
                        date_add(subdate(
                                date_sub(day_date, INTERVAL 1 DAY),
                                date_format(date_sub(day_date, INTERVAL 1 DAY),‘%w‘) - 7),INTERVAL 6 DAY),2) week_num,
                    in_weight,
                    out_weight
                FROM
                    day_weight_tb
            ) middle
        GROUP BY
            week_day,
            week_num
    ) result;

思路：先確定一天是屬於一年中的具體周數，再獲取到一周中的周末日期，最後根據周數分組求和。

MySQL按周統計 WEEK 實例