二百七十八、ClickHouse——将本月第一天所在的那一周视为第一周，无论它是从周几开始的，查询某个日期是本月第几周

一、目的

ClickHouse指标表中有个字段week_of_month，含义是这条数据属于本月第几周。

而且将本月第一天所在的那一周视为第一周，无论它是从周几开始的。比如2024-12-01是周日，即12月第一周。而2024-12-02是周一，即12月第二周

二、文心一言

文心一言的代码有点问题

三、SQL语句

select
    day,
    toDate(concat(toString(toYear(day)), '-', lpad(toString(toMonth(day)), 2, '0'), '-01')) as first_day_of_month ,
    DAYOFMONTH(day) - 1 AS days_since_first_day,
    toDayOfWeek(first_day_of_month) AS first_day_of_week,
    (7 - (first_day_of_week - 1) % 7) AS days_in_first_week,
    CASE
        WHEN days_since_first_day < days_in_first_week THEN 1
        WHEN days_since_first_day >= days_in_first_week  and days_since_first_day < days_in_first_week+7  THEN 2
        WHEN days_since_first_day >= days_in_first_week  and days_since_first_day < days_in_first_week+14  THEN 3
        WHEN days_since_first_day >= days_in_first_week  and days_since_first_day < days_in_first_week+21  THEN 4
        WHEN days_since_first_day >= days_in_first_week  and days_since_first_day < days_in_first_week+28  THEN 5
        WHEN days_since_first_day >= days_in_first_week  and days_since_first_day < days_in_first_week+35  THEN 6
    END AS week_of_month
from hurys_jw.tb_week_of_month
group by day
;

• first_day_of_month 计算本月的第一天。
• days_since_first_day 计算从本月第一天到目标日期之间的天数差。
• first_day_of_week 获取本月第一天是周几。
• days_to_first_monday 计算从本月第一天到第一个周一之间的天数（如果第一天不是周一）

四、验证查询结果

和11月日历一一验证，没问题，搞定！