mysql 的yearweek和DATE_FORMAT

2018-12-12 补充

php date函数 'W' 获取到的星期数，经测试发现相当于mysql yearweek函数的第二个参数为3的获取的值

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mysql的这个两个函数都可以用来计算一个日期所属周是该年的第几周，用于对自然周进行统计查询

1.MySQL 的 YEARWEEK 是获取年份和周数的一个函数，函数形式为 YEARWEEK(date[,mode])

例如 2010-3-14 ，礼拜天

SELECT YEARWEEK('2010-3-14') 返回 11
SELECT YEARWEEK('2010-3-14',1) 返回 10

其中第二个参数是 mode ，具体指的意思如下：

Mode	First day of week	Range	Week 1 is the first week …
0	Sunday	0-53	with a Sunday in this year
1	Monday	0-53	with more than 3 days this year
2	Sunday	1-53	with a Sunday in this year
3	Monday	1-53	with more than 3 days this year
4	Sunday	0-53	with more than 3 days this year
5	Monday	0-53	with a Monday in this year
6	Sunday	1-53	with more than 3 days this year
7	Monday	1-53	with a Monday in this year

 2、date_format函数不止可以返回周，也可以返回月日时

按周

select DATE_FORMAT(create_time,'%Y%u') weeks,count(caseid) count from tc_case group by weeks;

按月

select DATE_FORMAT(create_time,'%Y%m') months,count(caseid) count from tc_case group by months; 

按天

select DATE_FORMAT(create_time,'%Y%m%d') days,count(caseid) count from tc_case group by days;  

按小时

select DATE_FORMAT(create_time,'%Y%m%d%H') hours,count(caseid) count from tc_case group by hours;

二者在跨年时的不同表现

20181231是周一，现在我们执行跨年查询

这里需要注意上面对yearweek函数的第二个参数的解释，值为0时，这一周的Sunday在哪一年就将该周算给这一年

SELECT
    SUM(total_pay_money) AS money,
    YEARWEEK(pay_date) as date
FROM
    sy_day_pay
WHERE
    pay_date BETWEEN '20181231'
AND '20190105'
GROUP BY date;

第二个参数值为1时，这一周在哪一年的天数大于3天，就算给哪一年

SELECT
    SUM(total_pay_money) AS money,
    YEARWEEK(pay_date,1) as date
FROM
    sy_day_pay
WHERE
    pay_date BETWEEN '20181230'
AND '20190105'
GROUP BY date;

查询结果

然后是date_format的执行效果

SELECT
    SUM(total_pay_money) AS money,
    DATE_FORMAT(pay_date,'%Y%u') weeks
FROM
    sy_day_pay
WHERE
    pay_date BETWEEN '20181231'
AND '20190105'
GROUP BY weeks

 很显然，它将在同一周的日期分给了不同的年份

结论是当我们希望执行跨年的按周统计时，使用yearweek更合适，无论它将这一周给了哪一年，都是只生成一组数据，而不会变成两个