mysql 当前时间加3个工作日

1. 问题描述：

在日常工作中可能会遇到计算工作日的情况

2. 解决过程

(1) 首先制作一个假日表 holiday_config

CREATE TABLE `holiday_config` (
  `id` int(10) NOT NULL AUTO_INCREMENT,
  `holiday` varchar(8) DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC

其中id 为主键自增，holiday 为假期 格式为 '%Y-%m-%d' 

工作日：即不在 holiday_config 表中的数据

a. 增加的三天是否为假日，可能出现的情况有一下四种

        情况1 ：  如果无假日，则直接在原数据的基础上加三天即可，使用date_add(now(),interval 3 DAY);

        情况2：   增加的三天存在假日且小于3 那么直接用  date_add(now(),interval 3+（小于3的数） DAY);   

        情况3：  增加的三天存在假日且等于3 那么直接用  date_add(now(),interval 3+3 DAY);   

        情况4：  增加的三天存在假日且大于3 那么直接用  date_add(now(),interval 3+（大于3的数） DAY);

b. 如何获取范围内的假日数

假日数小于3 的情况

(SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN now() AND DATE_ADD(now(), INTERVAL 3 DAY)
 )

大于3 的情况可能有多种，目前只考虑连续假日小于等于10 的情况（具体看下方脚本）

(2) 最终结果

SELECT
    DATE_ADD(
        now(),
        INTERVAL 3 +
        case when   (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 3 DAY)
         )<3
        then (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 3 DAY)
         )
         when (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 4 DAY)
         )<4
         then (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 4 DAY)
         )
         when (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now() AND DATE_ADD(now(), INTERVAL 5 DAY)
         )<5
         then (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 5 DAY)
         )
         when (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 6 DAY)
         )<6
         then (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 6 DAY)
         )
         when (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 7 DAY)
         )<7
         then (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 7 DAY)
         )
         when (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 8 DAY)
         )<8
         then (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 8 DAY)
         )
         when (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 9 DAY)
         )<9
         then (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 9 DAY)
         )
         when (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 10 DAY)
         )<10
         then (SELECT COUNT(1)
         FROM holiday_config
         WHERE holiday BETWEEN DATE_ADD(now(),INTERVAL 1 DAY) AND DATE_ADD(now(), INTERVAL 10 DAY)
         )
            end
        DAY
    ) AS target_date;

3. 备注

目前只考虑连续假日小于等于10 的情况，如有问题请联系。